Apart from Bachmann what/where/who is a good source for buildings that fit the Thomas theme?
Thomas is British. So the best buildings are Hornby scaledale. Which are 00 scale, but won't look too out of place with H0 scale stuff. Tho if you get OO buildings, get OO cars and people too.
For Hornby stuff in America (technically here in Canada)
Model railway imports,
Brittania models
If you're in America, you need to rely on an online retailer. Hornby pulled their retailers out of the US just before Christmas 2011. In addition to the ones Shawn has, here's two VERY good ones:
http://modelfair.com/
http://ehattons.com/
Thanks guys that's a big help ;D