It's not a rag joint. I guess you can all it a collar.. Flaming river is probably the best place to find one, but it gets rid of the rag joint. (it will come as a universal joint instead of a flat piece of rubber)
I got mine from a car at the junkyard... I searched for a 74-78 mustang/pinto, 79and up mustang, 79 and up fairmont/merc. zephyr,
any of these cars that have a manual rack, will have the piece you need.
I believe the splines on the manual rack are all the same.
The flaming river part is better if you can afford it because it give you a more precise feel for the road thru the steering wheel. since the rubber rag joint is deleted. Best bet would to be to buy the whole new shaft that goes from the bottom of the column to the rack..
good luck