It seems that Toyota Camry is the only model being advertised for big cars.

 

Does anyone know where I can rent a Honda Accord - the 1998 model onwards ?

Try hertz I think they have Honda Accords.

The rental branches in Pattaya have whatever their pool of vehicles have and anything left from a rare one-way rental. I know Avis have the brand new, hybrid Accord as I got one from Suvarnabhumi a few months back. Since it's in the same class as a Camry, then it's pot luck on getting one short of specifically requesting that make and model.