I opted for the Surefire G2 Nitrolon as best for my needs when checking for the cause of security alarms going off.
I have the sling, light holder and rail from Kel-Tek. Two possibly usable 30 rd. mags are in transit. They fit a Beretta but there is no guarantee they'll work in the Sub. The price was decent so I grabbed them.
This place is invaluable for any Kel-Tek owner.