I doubt that you will find U-joints at your local auto parts house. I have heard that these half shafts were "borrowed" from some kind of Italian textile machine.
The Pantera vendors should have U-joints and half shafts. A couple of years ago Dennis Quella at Pantera Performance Center in Colorado quoted me a price - I think $60 each for U-joints. Call for a current price. Phone number is (303) 660 9897
My yokes were oversized, so I bought the Spicer Half Shafts from PI Motorsports. Check their website for a current price
http://www.pim.net/All of the Pantera vendors should have U-joints and half shafts. These were ones with the best prices when I bought mine.
Later I found that Atlanta Powertrain could put them together for $500 a pair. You may want to check for a current price. Ask for Mike Romine at:
Atlanta Powertrain & Hydraulics, Inc.
4491 Moreland Avenue
Atlanta, Georgia 30288-2146
Phone: (404) 361 2818
Actually it is in Conley, Georgia even though the phone directory says Atlanta.