You might want to also search for Stronglight 49D cranks/rings. For the inner rings, they used the same 122 BCD as their road doubles, presumably to save on chainring costs. The smallest chainring was a 38. I bet a bunch of 40s would have been used in the classic 52/40 x 14-17-20-24-28 'Alpine' double, as well.

39s might be a lot harder to find... I didn't start seeing 39t chainrings until the early 90s, when the 53/39 took over from 52/42 on road bikes. (Plus the bike industry has an irrational hatred of odd-toothed chainrings.)

TL;DR... You might have to buy a crankset.

--Shannon