Big Bear Engine Company in Denver CO might be one possible source. Not sure what kind of budget you have but don't expect it to be cheap. Complete engine runs around $8000 not counting shipping. On top of that you'll have to add any parts needed to fit your specific application. Probably an overall budget of $10,000 may be safe but it could get higher. Cummins sells complete crate engines for their new R2.8 but they aren't cheap either.
You might be ahead to look for an old Dodge with a 6bt with a 5 speed. You would have about everything you needed for a swap in one shot. You might have to get a drive shaft made for it and depending on what you are going to put it in you may have to do some fabrication/making parts.