> Air shifter
I never knew such a thing existed! So I guess you need something small that you can pack up when you ride in case you happen to run out of air out in the boonies. So it needs to be small, capable of over 100 psi and preferably 12vdc powered.
Have you considered something intended for bicycles? I see there are some battery-powered rechargeable ones available if you google "miniature electric bicycle pump".