I recently got one from Jess at High Angle Driveline http://www.highangledriveline.com/. He pretty much had the best price and a good reputation. You are going to have to take some measurement on the yoke to see what size u-joints you need. Jess can walk you through it.
Best price I found was at Jeff's Bronco Graveyard, but that was for a stock replacement one. I had one built locally (Billings Montana) with a bigger rear u-joint for less than the best price I found on the internet. I wouldn't discount locals. I had it done at a place that does welding and driveline repair and rebuilding for heavy trucks and so on. They had it done in 3 days.