I borrowed this idea from a toy my son has called a 'Saxoflute' and made the pieces to be compatible with it. I have mirrored some pieces and added several of my own design. The raised holes on the finger pieces make it much easier to play. The whistle part works fairly well but could perhaps be improved. I am not a trumpet player, but I thought having a trumpet-style mouthpiece might be a fun addition. The 180-degree and 45-degree pieces did not play well when printed--I think the inner surface may have been a bit too rough, not sure.
I would love to see others make creative additional compatible pieces, so please share if you do! One piece I have in mind to make is a trombone-style slide. Perhaps someone else can beat me to it?
Everything prints without supports except the 180 bend. That one requires a bit of support, but I was able to print it successfully using Simplify3D. All parts were printed in MadeSolid PET+ on a Type A Machines Series 1 (2014 model).