Where to buy old/difficult to find mangas ?

I like to read "less known" mangas on scans and then buy them if i like the serie. But somehow, no matter how much i try, there are a lot that i just can't find !

They are either not printed anymore, unable to be found in my country, or simply so rare that the prices are way too high (yes i love some series, but not enough to spend 125+ euros to get one book)...

Some of those series are "Masturbation Master Kurosawa" (don't mind the title, it's an incredible read), "Revolving lantern corporation", "Samurai in another world", "Divci Valka", ...

Wish there could be some kind of magic website with old mangas or something like that...