You could ask, but the Southwick hubs were a very limited production run, organized by the late "uncle jack" Drews. With only 25 sets made back in 2005 (AFAIK), I doubt there are any left on the shelf.
"To order, call Southwick Machine and Design, 309-949-2868."
I'll add that first one I tried did not run true. Probably just a burr under one of the bearing races (but why bother pre-installing the bearing races if you're not going to do it right?) But I'd had them on the shelf for several years, so I didn't try to contact Southwick to complain.
Revington probably has something, check their web site.
Another option is to reinforce the original type hubs. Here's a photo courtesy Jack Brooks.