That's one of the things that stopped me from ordering multiple sets at the outset, it seems like there would be a lot of redundant artifact dice.
I've now found a place in the UK that advertises custom, laser-engraved d6s (if you order at least 25) starting from 20 pence each. That's about the same price as TheDiceShopOnline sells blank dice for, so could be an option. On their site, they say that they are trade-only, but website of their retail stockist sends you straight back to them at the moment. I've mailed them a few questions about what they can and can't do and how much it will cost. I'll post some details here when I hear back if people are interested?