Originally, resonator guitars were invented for just this reason : cut through against competition from the brass section, without an amp..!. Worth a try, especially if the repertoire is suitable. One or two points to consider : many players use a reso guitar like a lap-steel; these models have a square neck profile, unsuitable for 'standard' guitar playing position. Look at models with a rounded 'C' or 'U' profile instead. Some models have a piezo mic built in, but more rarely with a pre-amp, which makes amplifying a little trickier, as either the amp has a piezo input, or an external pre-amp is required. The reso part of the guitar is fragile, so a stout case is needed for anything but home use. They're louder than a folk guitar, especially in the 'medium' frequencies, but won't fill a large hall unaided just the same. Trying a few models would be recommended; proces start at around £300 and go up quite quickly.
On the other hand, it's not uber-effective, but a piece of felt over the accordion grill could be tried to mute it a little..? Some folk remove the grill, line the inside with masking tape or similar, then put the grill back. Choice of register has an effect, with some 'bassier' registers being less strident. Other than that, it's just playing technique to play with less volume. Hope this helps; sounds like a nice project.