Keep Circulating the Tapes; DoDonPachi Campaign Version, a single board of which was distributed, and to a contest winner. As such, this version is not available in MAME, and if the board becomes damaged beyond repair, this piece of history (and arrange mode of DoDonPachi) is gone. Forever.
The retail version of DaiFukkatsu Black Label. Although the DLC version of Black Label is available in the PAL version, which has no region lockout, it does not have the the Ketsuicrossover arrange mode that the retail version has.
Irony: The Ketsui arrange mode's soundtrack was arranged by Jake Kaufman, an American composer.
SaiDaiOuJou, though at the least it is region-free.