Barbara Dennerlein made at least two solo organ CDS, one on a church organ, and at least one duo with Argentinian drummer Daniel Messina.
Jeff Palmer recorded his first album solo, on Improvising artists (click here) - AFAIK it is still available, if only on cassette and directly from him.
Clare Fischer did one solo LP for Revelation (Great White Hope! was the title - not a Hammond but some electronic machine he used, and two tracks on Rhodes piano), and one for MPS on a small baroque pipe organ in label chief Brunner-Schwer's posession (Clare Declares). Very nice and madly swinging record, which is very hard to do on a pipe organ.