There is a carryboy place on Petkasem near the shell station, sorry can't give better directions, but there is a sign on the building. They had a wide selection of different types, not sure if they carry it but worth a try. My wife bargained them down some when we bought our truck cap.
The proper function of man is to live, not to exist. I shall not waste my days in trying to prolong them. I shall use my time.
Carry boy are probably one of the largest manufacturers in Thailand of fibreglass canopies and sports lids I have attached a link to their website and they could probably advise you of a local agent.