Browning makes a screw-in hi-viz site that will fit any vent rib gun, including Beretta. You can also try the Browning "Bird Buster" magnetic light-pipe site. I got mine for $18.95.
Benelli - Cordoba (20 ga. & 12 ga.)
Browning - 725 Sporting (12 ga.), Maxus (Hunter & MAX-4 Stalker)
Franchi - Renaissance (20 ga.) <-- For Sale. PM me.