Great duet quiksilver, its on the British open 1996 cd, James Watson and Philip Smith playing it with dyke accompanying them. Another good SA duet is an oldy called
Always Cheerful, I have an old knackered cassette taken from an even older knackered LP of James Williams and Derek Smith playing it!
Also
Lover of the Lord and
Captain and Lieutenant are great fun too, slightly easier is
In shining armouror a duet called
Hosanna which is straight forward enough. Mentioning these brings back memories of a mis-spent youth where my father used to drill these into me on a saturday afternoon!!!!

memories!
I'm sure SPS or
www.worldofbrass.com will have many of these available if not now, but in the very near future.