http://www.worldclasscycles.com
http://www.aebikes.com
If it's just a road conversion, buy a good pre-built track wheel, such as a surly/ma3,
or a promax/open pro, and use a cheap front wheel and use old road cranks. You can really do it on the cheap. Make sure that you use a GOOD COG. using a cheap cog will ruin your hub threads, thus making the hub worthless.