I know of three other sites besides this one and ww.missingfabrics.com
www.fabrics.net - look on the left side of the page for where to post a request for fabrics - seems to be an active site
www.rjrfabrics.com - click on the "Fabrics" tab, then click on the "Fabric Finder" - and then click on "Make new request"
I think it's supposed to be only for RJR fabrics, but I've seen other requests on there, too
www.ladybuttonfabrics.com also has a "want ad" section - does not seem to be a very active site