I believe the sanwa buttons are 15mm from the lip to the bottom of the base
it is possible to mount them on thin lexan but you might need to reinforce the area a little with some bracing.
sheet metal can be purchased in various places depending on your area, the key is to find a sheet that will be rigid enough not to bow but depending on the area you'll need you might not need something of overly heavy gauge. here locally (toronto) we have metal supermarket (metal store) but in your area you might have something similar. Home depot also has some but I dont know the gauge of their stock. to cut holes theres a few options, you could use a nice high quality hole saw, Panel Punch (kinda costly but worth it if you do lots of metal panels) or even a Uni-Bit can work too provided the material isnt overly thick.
hope this helps
