Probably better to stick with a 6 speed with that spacing but there are plenty of options. SunRace has been mentioned a lot but I just bought a 7 speed IRD Cyclone I.
They make 5 and 6 speeds too.
The first one was faulty with horrible noises when freewheeling. The supplier, Soma/Merry Sales sent me a replacement and all is fine. Used with a modern KMC chain I have had a little "ghost shifting" but maybe that will go away with slight wear and my adapting to the set up.
Always loved buying NOS Sachs-Maillard and still have one but the notched teeth wear the chain plates. Always a trade-off.