Custom Drive shaft vendors
Look locally under heavy truck repairs. Those guys KNOW driveline work and normally it's a lot cheaper because for them it's light duty stuff.
Yes the local heavy truck repair shops usually may do driveshaft work...
But as you experienced with BIG ADVERTISING name shops, like them, some truck shops only know truck shafts.
What trucks experience aren't the same as what cars experience, like our local truck shop, i was there builder for all there shafts till they thought it would be more profitable for them to do it themselves, now they build shafts, but they aren't getting the knowledge from me, and they have had some issues.
Ask questions, and if they aren't asking you the right specific questions about use and quite a few other particulars, leave. . . . .
Unless you want to have a mishap like that girl in TX when her shaft came apart just after the line, broke her helmet, shoulder, face, collar bone, arm, 3 ribs, leg, ankle. . . . .