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...I am in the middle of building a bunch of wheels here, so I just bought 500 14G (2.0) and 500 15G (1.8) nipples at online retail prices.
Brand new, the DT versions in bulk are running about 40 bucks for 500 ( a little more for the 15's).

Those are the brass ones, chrome plated. I personally don't build wheels with the aluminum ones, because they have some issues with practical use of the wheel over a longer time period, and I don't look at the weight saving as an advantage in light of that.

I have some Bayard spokes left over here somewhere in the garage from an old restoration project. I don't know if they are the current standard threading or one of the older ones and won't fit a current spoke threading. If I get in there today or tomorrow I'll check for you. maybe someone else here remembers and can tell you.

Most people these days who have older stainless spokes with a non standard threading just cut them to length and roll new threads using someone's Phil Wood or similar machine. At least that's what I do. So if any of your nipples are a different threading I think they might be hard to sell without spokes to match. But some of the "period perfect restoration" people are certifiably nuts, so take what I say in that light.

I personally don't know anyone crazy enough to build wheels using galvanized spokes any more, but there are probably guys out there.