It if is was me, I'd see what you could find in the way of seats out of a salvaged EXL Canadian Accord. They have the seat heaters, so you could use stock parts and avoid compatibility problems (still would require some custom wiring at least though). One option would be to swap in the entire seat and switches and run power to the heaters. Another possible option would be to remove the seat heating elements and retrofit them to your seats. I don't know how easy that would be, and you would have to be comfortable with dismantling your own seats. But I would assume it could be done if you want it bad enough.

I've never looked into aftermarket units, but I'm sure there are some out there. I would guess the OEM unit would be more compatible, but who knows.

I swapped in leather 02EX V6 seats into my 99LX and ran power to them and it worked out great. If you are interested, search under my name and see the thread I posted in this forum when I swapped my seats in.