Greg,
Horace Silver Quintet & Trio is coming out in the Analogue Productions Hoffman/Gray reissues this August, so I would wait for that one.
Horace Scope and Horace Silver And The Jazz Messengers are both available from Classic Records and are not on the MM or AP collections lists that I have seen. Those are both good picks, and I may actually buy them with Classic going the way of the Dodo.
The Cool Struttin' in the Music Matters series is not mono to my recollection, and it is not listed as OOP. That is the one I would buy (and did).
Cheers.