They've certainly been available commercially at various points. If you search for microCHP, you'll find them. I can't see that any of the big manufacturers a

They've certainly been available commercially at various points. If you search for microCHP, you'll find them. I can't see that any of the big manufacturers are currently making them, though. Honda and Baxi used to have residential stirling engine CHP boiler models that seem to be discontinued. Currently, I think the Senertec Dachs might be closest to what you're after in size, although it's based on a conventional four-stroke, not a stirling engine. The residential CHP market seems to be shifting to fuel cells.