I did find one when googling trimmer capacitors on the Sprague website.265-880 pf 500 wv .Seems like it will work. Turns out Mouser is a distrubutor and the exact same part is the only part they carry in stock in that capacitance range.Go figure. Guess I got lucky for once.
Ordered it today. Will report back how it works next week when I receive it.