Ian,
I agree with the high costs. I sincerely hope you find a solution, but I must tell you that my experience does not make it look too promising.
I had searched for years for a B7 Ricky. Lo and behold I found one in very good condition. Good, except 2 keys. Both broken off. One the butterfly was gone; the other one, the gears would strip out as you tried to tighten the string. To make matters worse one of them was on the 3 side and the other on the 4 side. And this particular B7 uses the orginal 3 and 4 strip type keys.
So I thought this should not be too difficult. So I have several friends who own music stores. Would you believe both of them including another music store let me go thru literally barrels of keys. I spent hours and days turned into weeks.
I found every conceivable key strip ever built I do believe. Some of them looked like they may have come over on the santa maria with Columbus
NOT one would fit. NOT one. I called every where. The problem was a unique one.
1. Would you believe the spacing is NOT uniform on the 4 side strip? Well believe it!
2. The height of the peg and the diameter is so unique, I was not able to find a key in any style that would fit. NOT one.
Apparently my Rick was made with spur of the moment parts is the only rational I can come up with.
So I simply gave up. Until Wayne Tanner (Mr Jerry Byrd clone) sent me two strips that I could would work. They were pretty well warn and there is mucho backlash, but I am greatful to Wayne.
Apparently Rick was not that concerned about keys
The ONLY way I know of and it scares me to even think about it; is to use screwless PSG type grovers (like Emmons) with the short pegs and then have a very dedicated machinist VERY carefully mill about 1/8; off the thickness of the bakelite keyhead stock. Plus drilling the holes large enough to accomadate these keys.
IF this could be done without breaking the keyhead, it would not only be beautiful but allow any of the keys to be replaced easily.
But I simply cannot bring myself to let anyone do it. Ya jes don git a second chance on Ricks. So I live with it.
Now in your case you already use individual keys so at least that is one up for you. I wish you much success.
May Jesus bless you in your quests,
carl