There's plenty of choice:
Marc Reift offers a large selection of music here:
http://www.reift.ch - some of it good, some of it so-so. You have to order direct from them in Switzerland as, to my knowledge, there is no agent for them in the UK.
MF Music do a number of good quality quartets and are sold in this country by Mostyn Music:
www.mostynmusic.com
Obrasso also has a large catalogue of quartets which can be found here:
www.obrasso.ch - like the above two they are based in Switzerland but you can get their stuff from Studio Music in Luton.
Kirklees Music and
Glissato Music (Italy) also have small catalogues of quartet music, and there are many other publishers with a few titles available. You might also try
June Emerson, which has a huge catalogue, and also the online publisher
www.onlinesheetmusic.com which has a number of interesting items, although its search facility is less than ideal and you have to wade through pieces for all small brass combinations to locate the quartets - but some of them are worth it!
You can also find a number of publications for sale on Ebay but in my opinion they are not of particularly good quality.
Good luck
Jim
