I assume Para = Parabellum as in 9mm.
If its a preB, you hunt and hunt and if you are observant, you can find them at shows, or perhaps online. Some are sold on this site, but it will be expensive. They are MORE ROUNDED on the shoulders than the later B model mags. I can usually spot them from a pic.
Also, the +2 mags for the SP01 Shadow usually fit and drop free very well. Those are the least expensive option that works unless again, you luck out at a show. Old TA 84 and I think TA 88 mags work also.