Not single manufacturer, it looks like you have to get the runners from the same stock though.

US sleds are built by Geoff Bodine's NASCAR group:
http://www.wtnh.com/dpp/sports/olympic-bobsled-builder-leaving-conn

NBC's site talks abt min and max weight adn the origin of th runners:
http://www.nbcolympics.com/bobsled/insidethissport/equipment/newsid=257590.html