Have you tried all the normal freight carriers, Fed-Ex, DHL, UPS, etc.
Most of them have deals for space available, larger items, which will go when the aircraft is not maxed out.
You may need to box, or mount it on a sled, depending what it is.
I have shipped entire Helicopters, sets of Main Rotor Blades and various other large items with these carriers.
Call them and ask.