Complex sentence: There isn't a real R4 Series because the manufacturer of the R4 stopped producing them, but there are other cards that are of similar quality made by other companies (and thus are clones).
Split into simpler sentences: There Isn't a real R4 Series because the manufacturer of the R4 stopt producing them. But there are other cards that are of simmular quality that are made by other companies (and thus are clones).