Customer has switch plates made out of slate. They're about 3/8" thick. I've been using spec toggles from Hubble and Leviton, but they don't protrude out enough. Are there any switches out there that are a little more "well endowed"?

Most of the thick plates I see are the ceramic ones that people pick up at the local artisan shop, and they are 1/4" to 3/8" thick. I won't install them since I've yet to see one that's got any sort of approval...I will only install the standard approved plate, and what they choose to install after I leave is up to them. Saves a lot of headaches.

Have the slate beveled, around the toggle opening.

Take a grinder to the back of the slate plate. You should be able to take enough off so the switch will stick out plenty far enough. Saw this done in a remodel of a 1890s house here in Mass. That old sparky knew exactly what to do. Good luck.

Better idea.... Have someone else take a grinder to it.

LOL!