If you don't mind inauthentic, Unicomp will make that "I" key for you. IIRC, adding front-print to a keycap was not that expensive.
I asked them about it, and they said they wouldn't do it unless I bought a whole custom printed SSK set. I already have a US APL Unicomp set, so just looking to complete my original set. I know it's a long shot, but you never know, right?
)
I wish they would do the single key! They do single prints of normal keys..
It's not even a front print, just a second top print.
Thanks though!