I've been looking into this as weel because the only Guano I can get where I live is.
Guano Grow 10-10-2
Guano Bloom 1-9-1
So not muck K
I use mollasses to bump up the K
Also Dutch Master Potash Plus 0.7-4-11
these together round out quite nicely
Uncle Ben also says
Saltpeter 13-0-66 (from memory, but close)
Green river sand 0-0-3
Sulphate of Potash K = 66 also 22 sulpher
Anyway, that's what I've come up with, if anyone knows more then please tell us.