I don't know if this was mentioned or not, but I found two different websites that all together have a HUGE collection of TMNT gifs. Altogether there are probably over 300 gifs!
http://originaltmntgifs.tumblr.com/
(About 10-15 gifs from the OT)
http://tmntgifs.tumblr.com/
(The motherload of TMNT gifs, that contain GIFs from all the cartoons [OT, 2003, CGI 2012], all video/arcade games, movies [all live action and 2007 CGI], and one or two from the anime.)
If you want to preview ALL the GIFs on one screen...prepare yourself! LOL
http://tmntgifs.tumblr.com/archive