The TM tri-shots are indeed hard to fix. I once purchased a broken TM benelli shorty and it took me two weeks to get it running. One of the nozzles broke and jammed the mechanism. I had to make one out of copper and glue it in place. Assembly and disassembly of the gun is a painstking process, but if You have time and patience, it is possible to do it.
Usually, they jam because bb's gets stuck in a space between the three nozzles (dunno why they left the space there in the first place ;/)
The mechanism looks like this - pic 2 (found it on the web, looks like somebody's upper nozzle broke like the one I fixed did)http://t3.gstatic.com/images?q=tbn:ANd9GcSBuxKcX4cQYwhZvf4ttLf6J2HNjCEUK8f2e4jjQZJGJERwsYZn9JCrcQkV
Try this, usually helps when my benelli jams:
-remove the shell
-try to shake out bb's out of the mechanism through the ejection port
-try pumping the gun, if it won't lock DON'T PUSH!! (might break the nozzle)
-give it a solid whack in the rear with your hand while pointing the barrel down(might get the bb's out of the mechanism
-try pumping again, facing down
-repeat many times
If that fails, try fiddling with a cleaning rod or a long thin wire with a tiny hook, visualize the insides and try to pry out the bb. Then repeat shaking-pumping.
If THAT fails, and You find nobody to fix it, try opening the gun. But be warned, it is a pain.