Okay, I'm baffled- how can it be a ball and trunion, AND a slip joint?
And yes, parts are out there, but far and few between, and pricey when you do find them. You got lucky, most driveline shops want nothing to do with B&Ts, either because they can't get the raw parts or they just don't want to deal with them.
That's why I recommended the conversion shaft- That REPLACES the B&T with a slip joint and a U-joint.