From the Yahoo Critterslist, some links for motorcar (speeder) information:

Anyone who is interested in speeders/motorcars/jiggers should check out the
following sites:

Motorcars, Inspection Cars & Speeders at:
http://pw1.netcom.com/~wparsons/index.html

The Railroad Motor Car Page at:
http://users2.ev1.net/~cleveland/speeder/speeder.htm

The North American Railcar Operators Association at:
http://www.narcoa.org/

The NARCOA Personal Motorcar Site at:
http://www.narcoa.org/personal.htm

PRO Online Sales at:
http://www.pro-online.org/ads/4sale_want.htm

North Central Railcars Ltd at:
http://www.whrc-wi.org/ncr/

Ohio Valley Railcars at:
http://members.aol.com/wm340/myhomepage/business.html

Roger's World of Railcars at:
http://rogerwld.railfan.net/railcar/railcar.htm

Not sure if these will come up as active links, you might have to cut and paste.

Also on the Pacific coast, Motorcar Operators West:

http://www.mowonline.org/