uhm...maybe this can help...i remember on the map Andersen Ground war, there was a static MG (M2), but he added the cannon from a ZSU-23...well, you didn't "saw" the gun itself, but it was able to fire.
So maybe you can create a static MG and use addweapon to put a minigun in there.
I just checked some addon sites...didn't found any...maybe you should head over to the Addons: Ideas Forum and launch a request there ;D