I work at Dusty Strings in Seattle. We carry some phosphor bronze and brass wire in 30 foot and 50 foot lengths. I don't know what all sizes are there. Call 206-634-1662 or send email.

Have you considered using individual loop end strings throughout the instrument instead of coils of wire that wrap around and form two or more strings? You may find it easier to deal with when it is time to tune the instrument, and especially when it is time to replace strings. It also allows you to use wound strings for the bass notes, which you might like better. Although if you decide you like the PB or brass strings better, they can be more of a hassle to get with loop ends. Dusty Strings sells a few sizes of PB wire with loop ends, but not any brass. Brass strings break with startling regularity anyway.

John Peekstok