http://cgi.ebay.com/ebaymotors/GM-Transf...=item5ad25f5ec7For the Timken T-221
The hubs are NOT Warn. They are GM. They are not reproduced. It would very acceptable to put on a pair of Warn hubs. They will probably work better than the originals anyway. I found an NOS one to replace the right side. That was on EBay many years ago. You might get lucky, you might not. Most stuff becomes available, it just depends on how much and how long you'll wait.
Also, a bit of clarification on "k" numbers. If you have a 61 K15, that is a 4x4 (K) longbed (15). A shortbed would be a K14. If you are doing searches for parts, You would refer to your truck as a K10, not a K15. No one lists anything for a K15. Obviously a K20 is a 3/4 ton truck. The K10 hubs are different from K20 hubs not only for the bolt count 6 vs 8), but are a completely different design.
Something like this may work for you, but don't take my word for it-do your homework. The stock front axle on a 61 K10 is a Dana 44. (44.5F)
http://cgi.ebay.com/ebaymotors/NEW-WARN-...=item27ac9258df