What do you generally listen to yourself? Or if you've ever watched a movie that had a soundtrack you liked, maybe try for that!
I make my own kur music just for fun, and I've made one out of the songs by Múm, one based off of Black Beauty's soundtrack, and one from Totoro's. If I ever make it to Grand Prix, I'd make one from Sigur Rós composures. <3
If you know of any instrumental bands, or if you can find/the composer of your kur is willing to make instrumental versions of any song for you, remember this: do something different! There's plenty of musical resources out there, many are much more beautiful, catchy, and fitting to the horse than what is commonly seen, and you're less likely to have the same music as somebody else! ~
Maybe try searching "Yanni" on YouTube, though. He's popular in Europe, but his music is fantastic.