Sn3 Track
Currently, only P-B-L produces flextrack (code 70 and 55) and turnouts (#6, including the stub version). A lot of Sn3 modelers hand-lay their track. One person noted that if you are having problems curving the P-B-L flextrack, spray some Windex or similar window cleaner on the track, which acts as a lubricant without leaving a greasy residue.
The minimum curve radius can be as tight as 28". Modelers have reported that their K-27, K-28, K-36, K-37 engines can make those curves, but you will likely need to modify the pilot and trailing truck clearances. This is because, in Sn3, models are made to match the prototype, and not necessarily to work correctly on your layout.
Fast Tracks
If you don't want to completely lay your track by hand from scratch, Fast Tracks offers a number of aids to help you. First, we would highly recommend that you download and print their printable turnout templates. These are very useful in helping you plan your track arrangement, even if you do not plan on using the Fast Tracks jigs or aids. See their web site for the various templates that they offer for free (you will need a software application to open up the PDF files, and access to a computer printer to print them).
QuickSticks
The company offers their QuickSticks system for hand-laying ties. They are available for fixed straight track, for curves, for turnouts, and for wyes. See their web site for all the possibilities.
SweepSticks
Their SweepSticks system allows you to make straight or smooth-curved hand-laid track. These aids can also be used for laying out a track plan, first. They are available for a number of different lengths or radii. See their web site for all the possibilities.
Straight Track Fixture
You can build your track on the workbench, effectively making your own sectional track system, using their Track Fixture system. They are available for three rail sizes, and for straight and curved tracks (various radii), and for turnouts and wyes. See their web site for what is available. The jig may appear to be expensive, but if you need to build more than a couple of uses of that track, you will find that the jigs quickly pay for themselves, if you have the ability to solder and a bit of time. Note that the curved-track fixture, for example, includes three different radii in one jig.
Trifecta
The company's Trifecta Sn3 gauge is important for making sure your track remains in gauge as you attach it to your layout, module, or diorama. They have two different ones available (see their web site), depending on which size rail you use. You will definitely need these if you hand-lay your track without using their jigs.
SpaceGauge
Their SpaceGauge jig (see their web site) allows you to properly space parallel tracks together. Various spacer sizes are available.
Micro Engineering
Micro Engineering manufactures rail in various code sizes, both weathered and unweathered. Although the Fast Tracks jigs do not support it, Micro Engineering also makes code 40 rail, if that is of interest to you.
NASG
The NASG, itself, carries the NMRA Sn3 track gauge via our online store. We offer a discount, if you are an NASG member. If you are an NMRA member and not an NASG member, you can order the Sn3 track gauge via the NMRA's web site for a similar discount.
P-B-L
P-B-L is the main Sn3 manufacturer. When it comes to track products, they carry flextrack and turnouts. They also carry Sn3 track gauges.
Railway Engineering
Owned by an Sn3 modeler, Railway Engineering produces turnouts to your specifications. They carry track gauges.
Simpson Models
Simpson Models manufactures Sn3, S, and S/Sn3 (dual-gauge) brass roller track gauges.
Trout Creek Engineering
Trout Creek Engineering offers pre-built Sn3 turnouts (including stub turnouts) and wyes in various frog numbers with rail code ranging from 55 to 148.
Turntables
Millhouse River Studio, who specializes in high-end O-scale turntables and transfer tables, state on their web site that they can manufacture any of their turntables for S-scale as well.
Diamond Scale lists a 65-foot Sn3 turntable.
New York Railway Supply manufactures a turntable control system (independent of scale). The owner is an Sn3 modeler.
In 2017 Dallee Electronics introduced their turntable indexer.
With a little bit of creative effort, some modelers have taken turntables that were intended for scales other than S, and made them compatible with their S-scale layout.
Resources
The NASG developed a standard for track. You can read all about it on our Engineering Standards page. By having a well-known, publicly-available standard by which manufacturers can produce their products for S-scale, we ensure compatibility between brands, so that you can buy track from one manufacturer, and be assured that the locomotive that you bought from another manufacturer will run on that track with freight cars you bought from yet another manufacturer. If you are going to hand-lay your track, be sure to study those standards.
Rick Blanchard has a wonderful web page that lists track spacing, rail sizes, brake piping, and other dimensional data, including for S-scale. He also has a web page listing how rail sizes related to the various scales, and another web page on how prototype track curvature relates to scale proportions. There is also an Excel data file listing how real world dimensions translate to S (without having to pull out the calculator).