Welcome to the bolt, from Kansas City, KS.

I don't know about the best, however here are several links for aftermarket truck parts suppliers, that sell front drop spindles:

www.lmctruck.com
www.classicparts.com
www.bowtiebits.com
www.oldchevytrucks.com
www.brotherstrucks.com
www.earlyclassic.com
www.classicperform.com

This should give you a good place to start. Good luck with your search.

Tony