It looks like you need the entire magazine catch assembly. Part #29 is a disconnector spring. Do you know how to install it? There is no part #52. Grip screws are available from Bersa, and are listed in the parts list you've provided a link for. If Bersa doesn't have a part you need contact either Numrich Gun Parts, or Jack First Gunshop.
Jack First Gunshop - First in Gun Parts - Rapid City, South Dakota
Many times each of these companies has helped me out with hard-to-get parts; and I highly recommend them. No on-line ordering, though. You've got to use the telephone.