Tim,
Find the part number (in the Parts Catalog - Old Online Chevy Manuals) and
try to search for it here.
I do not gamble, but I'd bet is is no longer available from GM.
There are, however, a few GM NOS parts vendors with on-line catalogs. I cannot find a URL. A few years ago, I found 50 NOS, GM/GMC-only, big-bolt wheel nuts.
I'll look tomorrow (but, I still doubt you'll find one).