The creator JAM has several conversions of the SNES Tournament Fighters stages available for download at his website:
http://jamugen.blog103.fc2.com/
Also, Mugen creator MackX has a pretty fantastic Neon Night Riders stage he released recently. I highly recommend you grab this one
http://retrostage.trinitymugen.net/
As for characters, Casey Jones by Pioupiou (I think you have to extract him from the fullgame port to get him into your personal Mugen)-
http://pioupioud.cjb.net/
Apparently a Raphael was created a couple years back by Franco[8a] using the SNES Turtles in Time sprites, but this seems to still be in progress and pretty unpolished as far as gameplay. Not recommended.
There's a handful of Psycho Shredders that are floating out there, but these are incredibly broken uber cheap AI conversions. I might be able to pm him to you if I still have a copy in my files somewhere.
I'll see if I can't find out more info later on
EDIT:
There's a pretty cool Leonardo that uses the sprites from the 4-player 1989 Arcade game here:
http://sites.google.com/site/oldschoolmugen/Home
And you can download Karai and Armaggon from Infinity Mugen Team, you just need to register first:
http://www.infinitymugenteam.com/
Raphael & Donatello by Erradicator:
http://www.presstart.cjb.net/