STC for mogas in O-235

Hi everyone. I was reading about Petersen's STC to use mogas in the O-235.
Apparently the STC for the O-235 only allows premium (91 octane) to be used.
I would still be reluctant to use premium since it is a "step down" in
octane for the O-235. I would not have a problem if I was flying an O-200
and could "step up" to 87 octane since the engine was originally certified
to run on less.

Has anyone ever found premium available for aircraft use at an airport? To
tell the truth, I have never flown into an airport with mogas available.
The chance to cut down the cost of flying is appealing to me, but not if it
means the inconvenience of having to refuel from gas cans.

Matt