Where can I find a wall plate for this weird three-gang combo?

That rotary dimmer is designed to mount behind a standard toggle switch opening, which is why you aren't finding a specialized 'dimmer' hole in the wall plate catalogs. The skinny metal stem is built to center itself perfectly within that rectangular toggle slot. Once the plate is screwed on, the knob just pushes back onto the stem and hides the entire opening, making it look like a custom fit even though it's using a generic layout. What you're looking for is a **3-gang wall plate** with a configuration of duplex-toggle-toggle. The outlet on the left uses a duplex opening, and both the center double-toggle and the right-hand rotary dimmer will fit into standard toggle openings. You might see this listed in catalogs as a '1-duplex, 2-toggle' plate. It's a very common combination that any big-box hardware store will have in stock, ussually in the electrical aisle near the bulk contractor packs. If you find that the center switch is actually a 'decorator' style (the large rectangular rocker), the search changes slightly. But based on you describing a double toggle, the standard toggle openings are the way to go. Just make sure the devices are screwed into the box straight before you try to put the plate on. If that dimmer stem is even slightly off-center, the knob will rub against the plate or won't click properly when you try to turn it.

Since this is a kitchen, you shoud also double-check that the outlet on the left is actually a GFCI if it's near a sink. If it's just a standard plug and you're already opening things up to swap the plate, it might be a good time to upgrade that device for safety. But for the plate itself, just grab a standard white or ivory 1-duplex 2-toggle cover and it'll snap right togather.

Totally agree on the 1-duplex 2-toggle layout. I've run into this exact setup in older kitchens. One small thing to watch for—make sure the hex nut on that rotary stem is snug against the strap before you put the plate on. If it's loose, the stem will shift every time you push the knob, and eventually, it'll crack the plastic on your new cover. Also, since you mentioned the wall was just patched, grab the 'mid-size' version of that plate instead of the standard one. It gives you an extra quarter-inch of coverage to hide any messy drywall edges around the box.

Regarding that middle device, if that "double toggle" is actually a horizontal duplex switch where two levers occupy a single gang, ensure the mounting strap is perfectly vertical, as even a minor degree of tilt will be exacerbated by the rigid geometry of a 3-gang plate. I woud strongly reccomend opting for a flexible nylon wall plate over the cheaper thermoset plastic versions because, given your mention of recent wall patching, any slight surface irregularities or protruding drywall mud around the box will likely cause a brittle urea plate to hairline fracture the moment you torque down the center screws to acheeve a flush fit.

Oh wow, I had no idea that little metal stem was supposed to just sit behind a normal toggle hole. I feel like a bit of a dummy now for searching for a plate with a tiny circle in it! One thing I'm confused about though—you mentioned the 'strap' and a 'hex nut' for the dimmer. I don't realy know much about how these are held togehter. Do I need a special wrench to tighten that nut before I put the plate on? Also, if I decide to swap that outlet to a GFCI like suggested, will it still fit that '1-duplex, 2-toggle' plate or does a GFCI change the shape of the hole I need?