Carl Stamitz wrote 11 clarinet concertos, but only a few chamber pieces featuring the clarinet. However, his Trio in G, which calls for two flutes and a violoncello, is a lovely piece that fits the clarinet perfectly once transposed a third lower.
My arrangement for clarinet trio (2 Bb clarinets and a bass clarinet) was released last week, you can purchase the PDF files or the paper sheet music on Klarthe’s website.
You might also be interested in other sheet music:
Haydn – London Trio #1 for 2 Bb clarinets and 1 bass clarinet
Schubert – String Trio D471 for 2 Bb clarinets and 1 bass clarinet
Bach Concerto in D for 2 violons – arrangement for clarinet quartet