CVS, KB Toys, Wal-Mart and the list goes on. I've been pleased with 99% of the 1/18th scale bikes
Like these...

http://www.joedios.com/dioramas/sho...r&imageuser=183

http://www.joedios.com/dioramas/sho...r&imageuser=183

http://www.joedios.com/dioramas/sho...r&imageuser=183


The best ones are OCC and West Coast Chopper motorcycles. They're a few dollars more, but are awesome for Dreadnoks