the only legally sold lunar rocks went to auction a few years back for ~$900k for like 0.0007 ounces - they were three teeny tiny pebbles brought back from something like an early (60’s) Russian lunar lander and auctioned out of the estate of the former Russian space program head (or some such Russian tomfoolery)
Enough material then for even one sub-dial, as you say, might be pricey.
That said, an interesting quandary of law is arising as a result of the increase in commercial space flights - and it needs address soon!