My original cataloguing becomes increasingly inaccurate. Having said there was just one recording of the Trombone Sonata, op.172a, I found out about two more in a single night.
Carsten Svanberg and Bernadette Binder perform the sonata on an album of Classical Sonatas for Trombone and Piano published back in 1998 (Amos CD 5872). Other composers represented on the album are Hindemith, Frank Martin, Bentzon, Schmidt, Larsen and Sulek. These days, it appears the album is most readily accessed from the record company's own website (www.blasmusik.ch).
The other performance is by Roger Verdi and Martha Locker, on album called Almost Home - Works for Trombone (Greenmill Records). Other composers are Guilmant, Barat, Bassett, de Frumiere and Sulek. Known sources for the album are Amazon and CDBaby.