I’ve just uploaded a new arrangement, a trombone quartet transcription of the Kyrie from ‘Missa Pro fidelibus defunctis‘ (by either Antoine de Févin or Antoine Divitis - nobody is sure!).
This is a lovely piece of Renaissance music suitable for players of all abilities, although the top part will require some stamina in the mid-high range. It is also suitable for euphonium quartet or other combinations of low brass, just get in touch if you require different parts/clefs.
Get it here:
https://butemusic.com/downloads/kyrie-for-trombone-quartet/
Also available is the Introitus from the same mass:
https://butemusic.com/downloads/introitus-for-trombone-quartet/
I also highly recommend this incredible recording of the whole requiem from Marcel Pérès’ Ensemble Organum.