This website has paper pieced instruments:
http://www.heleenpinkster.nl/English/Archive_2008.htm
http://www.heleenpinkster.nl/English/Archive_2009.htm

try fabric.com

go to www.equilter.com and look for music fabric. They have a great variety of colors and patterns. If you google music fabric you'll find plenty. I made a music quilt for my daughter, a high school band director, and used a 7" treble clef stencil in the quilting design. It came out great.

I made a quilt for my daughter who was on the drum line in her school marching band. She also played sax and piano. I found marching band fabric that I cut for the border. Like everyone said, music fabric is hard to find it took me a long time to find it. I also bought light sensitive fabric squares, laid her sticks on them in the sun and placed the blocks in the corners. They turned out so cool...Good Luck

This store had a lot of musical instrument fabric when I searched before :D:D:D

http://www.jandofabrics.com/

I think I just saw some at Joann's yesterday? May try there! Or Fabric Lovers.com?

I got several fabrics for a musical quilt on J & O Fabrics