Luxembourg francs in antique markets

Recently, my son has started collecting banknotes and coins from around the world. In other cities, there are often specific markets for stamps and numismatics. I’ve been living in Luxembourg for two years, but I haven’t seen anything like that here. Maybe the antique market at Place d'Armes?

We’re not interested in buying online, part of the experience is finding the market, seeing what’s available, and talk with the sellers.

Any recommendations?

Thanks!!