I think there are a few that do TTM's. I have seen some threads on this topic here in the past, but fairly limited. I have sent TTM requests for Brewers a couple years prior, but none in the last 9 months or so. I think some of the sites are more geared on TTMs than here it seems. Sportscardforums has a TTM area or the website sportscollectors.net is a site solely for sports TTMs. I am a member over at sportscollectors.net and it is pretty active on autographs. They have both a free and paid membership. The paid membership is $15/yr and gives you access to tons of sports autograph and TTM information.
Hope that helps.