how rare is my 1938 Primus 991?

As in the title, I can't find many around to use for spares, are they a rare model these days?

 

I certainly wouldn't call them rare. It all depends on which country you're in. The further away you get from Sweden the fewer there are. If you need parts it might be a good idea to ask about them here or put an add in the wanted section. I'm pretty sure some of the Scandinavian collectors can help, or at least point you in the right direction.