I assume you are meaning plastic or laser-cut wooden models. I looked very seriously at this back in 1999 and 2000 and occasionally since and I have found very little. Walthers catalog has a lot of buildings http://www.walthers.com/
. If you wanted a German Main Street you would have more luck as modeling seems to be more popular over there. Otherwise there is a building here or there that may give you some of the look of Disneyland's mainstreet but not a lot that is close to what is actually there. I gave up on trying to find models that I could kitbash to look like Main Street myself.
If you want buildings that look like those on Disneyland's Main Street, then I would go with "paper models." You can make these more durable based on the "papers" (card stock or heavy weight papers) and by spray coating them in plastic. The Disney Experience is a great place to start http://www.disneyexperience.com/lvdlabs.html
. They have links to their models (many of which are free and they also sell CDs with models on them). If you are handy with computer graphics software (I use Photoshop), you can scale these models to HO scale. Their Castle and Main Street station are pretty details and reasonably accurate (I compare the castle and MSS to blueprints). There is also an incredibly good Haunted Mainson model available at Haunted Dimensions (there is a link to it on Disney Dimensions). There was someone that sold some lesser quality paper models (not as accurate and simplier/more flat) on Ebay from time to time that he called "Theme Park Models" but were obviously of Disneyland's Main Street.
My hope is to build a "paper model" of Main Street based on some photos I composited together back in 1999-2000. I also kitbashed two train station models to build a MSS back in 1998. You can see some of the things I have done at http://www.fototime.com/inv/643F78A06325765
Anyway, if you let everyone know a little more about what you want to do then maybe they can be of more specific help.