Steve,
Rich Bontempi @ HPH in SF Bay Area sells billet repro ones which are good for everyday use, & may have some NOS in his stash if you're looking for CW level. Same caps were used on Pedrinni, Mahle 4-lug & Fuchs 2L alloy wheels as OEM.
There are also several on TheSamba.com who sell the billet type, which will hold up to the apes with mallets at most tire shops!
Originals were pretty thin walled & subject to denting & deformation, are fairly costly now - so I'd suggest only you installing those for show use only - if that's your thing.
I have a set of each for that reason, originals are still NIB until I show 1st time!