I am having a devil of a time locating 2.5" electric engine instruments with a
270º sweep. Anyone know a reliable source?

Van's Aircraft has a full line of 2.25 inch gauges, and that is the
standard aircraft size.

It's not at all clear to me that 270 degree sweep gauges are the best
from a human factors point of view, however. Sure, if you need to read
things to an umpteenth of a per cent, the extra arc is nice, but that's
what digital is good at. My guess is that 90 - 135 degrees of swept arc
are easier to read quickly.

Ed Wischmeyer