Two 1967 LPs for Capitol, Presenting Rubin Mitchell and Remarkable Rubin, and an earlier self-released album on the Starmaker label, The Golden Hands of Rubin Mitchell, appear to be the pianist's entire recorded output. There were some singles on Capitol as well but as far as I can tell most, if not all, were tracks taken from the two albums.
According to the Schenectady Gazette newspaper of March 7, 1967, Mitchell was playing in the Albany-Troy, New York, area before being signed to Capitol. That's where his debut LP Golden Hands was recorded. After making his Capitol recordings he played in several New York City clubs and bars, then seemingly disappeared from the music scene. There is little information about him on the web.
Below is a link to a track from his first Capitol album, Presenting.
What Now My Love
Rubin Mitchell's version of Mas Que Nada appeared on Bossa Novaville, Vol. 14 of Capitol's Ultra-Lounge series of CDs. It's still in print and easily obtained.
There is a Mitchell collection called HiFi Hits available as a download. However, its cheap looking cover makes its origin a bit suspect.
Although these are tracks from his Capitol recordings, this release certainly didn't orginate with that company. Listening before buying would be a good idea.
Here's another Rubin Mitchell track, taken from YouTube.