There's one that advertises in every issue of Garden Railways magazine called Riding Railkits. Their web site is http://www.ridingrailkits.com and they are in Ontario, Canada.
there are also two magazines devoted to this subject:
Grand Scales Quarterly: http://www.grandscales.com
Home Railway Journal (this is a new publication): http://www.homerailwayjournal.com
Rene Schweitzer
Classic Toy Trains/Garden Railways/Model Railroader
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