Supplies

If you have a local hobby shop that deals in model railroad stuff, craft store can supply trees, bushes, etc.  I know Hobby Lobby caries that kind of material.  Micro Mark has extensive model rail and dio materials.

As for plastic rail, nothing comes to mind, but you can get formable sections in various scales, metal with ties, but don't know about "O".

Pick up a model rail magazine and check the ads in it for other suppliers.

Micro Mark is good, and so is Walthers. Woodlands Scenics is a good brand and easy to find online.

1/48 railroad stuff is US O Scale, but O Gauge comes in a range of scales.

 European will be bigger scale. The evil genius in model railroad scales is that there are a small number of different track gauges, usually metric in origin, and modelers back into a model scale by using available track and scaling the gauge of their prototype. 

AFA available track, don't be afraid to lay your own if it's not complex or involves turn outs.

Atlas make O scale 2 rail flex track.

Cool, thanks for all the info. I realized I might have been a bit confusing before; I'm not building railroads per se (mostly aircraft and armor), but do want to incorporate e.g. some trolley tracks and stuff like that.

I will check out the resources mentioned. Thanks!

There's the rub.  The model railroaders out there want either nickle-steel or brass track (for electrical conductivity) in O (or 0) guage layouts.  So, that's probably what you'll find out there.

Now, I want to remember that Plastruct had a rail section (for overhead crane tracks) in their line--but, that was long ago, and may be out of stock.

Trolley tracks are largely "buried" into the streets they traverse, so you might be forgiven for using a plastic "I" section sized to be close to the top of the rail, and let the rest sort of "vanish" into the space in the pavement/cobblestones, etc.

However, the bress O guage rail is pretty reasonable, and very forgiving.  There are "rail brown" patina chemicals available for those, too.

Afraid ki can't help you with stores as i am in the UK. But for ground work i mainly use woodland scenices and greenline materials. Woodlan makes a good selection of flock and scatter materails which if used right look nice. Greenline makes a range of tufts plants and other materials. I build in 35th but these can be used for variying scales.

There is one site in the US i have used called scenic factory, might wnat to check them out.

Thanks for all the replies, folks. Lots to check out.