I searched for a sub awhile back and decided to stay with the OEM. It was easier to find and not a long wait.
I see it is about $7 on Amazon with free 2day Prime shipping.
I have used this site for all three filters and plugs:
Onan Store
Jan and Rocky
Volunteers for USFWS. 29 refuges with 9300 hrs ea since 2006. 2004 Allegro 30DA, Workhorse 8.1, Banks, 2012 Jeep Liberty Jet, Blue Ox Aladdin, Brake Buddy Advantage Select, 300 watts solar, 5 Optima group 31 AGM's, 2000watt Ames PSW inverter.