As Neal told you Buchanan sells the parts you need.
http://www.buchananspokes.net/

Or you can have Lowridertommy handle the whole deal and send you the finished product ready to mount.
For me, I would just cut the hub from your existing wheel and mail it to Tommy. Click on his avatar to get his profile which has a link to his website. He will do it all for you and send you a ready to roll 21" with the hub you sent him. Affordable too! While you have the hub out you should have it polished or powdercoated. Only a few bucks more and you'll have a superb final product. If you want easy maintenace, go powdercoat.

"In the wind, with my mind on my money and my money on my mind"...now I just gotta get some.

Check out my world at http://jpswino.u.yuku.com/