I would look for an Oboe Duet & play the part on C trumpet..
A lot of the Baroque stuff has been transcribed to Oboe, and Flute but it also works well on C, D or Picc trumpet..
I'll look around & see what I can find.. One thing that comes to mind that might be fun is the Vivaldi for 2 trumpet in C..
You can find a midi of it here:
http://www.geocities.com/trumpetmidi/
Kevin