Front driveshaft double cardan centering ball: where to buy?

I'm changing the u-joints in the front driveshaft and stumbled on the centering ball, which I didn't know existed. Looks like a few rollers got loose in the process, but I figure I should replace it anyway as I'm changing the u-joints. Advanced auto didn't have one. They can order a service kit, and they list an "assembly" that they don't carry. Anyone know where to get a replacement? Shoud I get the kit or assembly?

Since it's just the front driveshaft I'd like to just order the part online, but I'm not sure where to look. Thanks.

http://www.stu-offroad.com/axle/driveshaft/driveshaft-5.htm

The local clutch, u-joint and driveline shop had all the rebuild parts in stock.

any drive shaft shop should have it on the shelf

Thanks yall, found a shop that had a "rockford" brand assembly for $45.