Such place indeed exist and it is called Bricklink, a website dedicated to trading LEGO items. It has extensive history and great catalog of LEGO items found on the internet. Prices and quality are, usually, far better than you would find on eBay. And as an extra bonus, there are sellers from all over the world, so you are not limited to you own region.
As Dan noted in the comments Bricklink catalog contain all types of 9V train tracks you are interested in for sale both in Dark Gray (older) and Dark Bluish Gray (newer) colors.
Edit. Upon further investigation decided to clarify situation in terms of custom tracks. While there are few 3rd party companies producing LEGO-compatible non-9V train tracks there aren't as much options with 9V ones. ME-Models used to produced some, but the company is gone now. FxBricks has shared their plans to introduce 9V tracks at some point the future.