Elizabeth, since you have a time deadline for your Masters paper , and probably need to include sources to verify your material, and you mention “published or unpublished”, consider this option: In your 15 years of being a harp professional, you surely have been influenced, and taught, by a number of harpists. Contact some of them and tell them you would appreciate it if they would write a few comments on your subject that you could then quote in print. You could even give a short list of questions to get them started. In return you would give their name as the source of this helpful information. Those harp teachers and performers might be glad to share a few hints. Best, of course, are the published texts such as the ones above,which might arrive to you in just a few days by priority mail. Probably other hints from pianists would be found using “Improvising” in a search engine, on the Internet.