Ack! I know someone on Dakka had a few hosted somewhere, but my memory fails me.
Honestly, though, it's dead easy to make your own gradient with a decent drawing/photo manipulation program - if you're looking for a backdrop for photos, you should probably already have one

. If you don't, I recommend GIMP (it's the free, open-source alternative to Photoshop). There's a large support base that has put out tons of tutorials. I'm sure you could find one to suit your need, if you don't want to figure it out on your own.