This isn't what you were asking for, but I use Ritter
SwordSteel strings on my
7, and they are wonderful! I've had them on now for about a month, and I like them more and more.
They are expensive though.
You could, in a pinch, get a six string set (or even a 5) and add guitar string(s) - they can be used if you put it through a bass string ball so it'll work with the bass bridge. Make sure it is long enough for a couple of turns around the tuning peg though.