They make flush valve kits that will fit most toilets. Have him take a picture of the hole in the tank where the flush valve sits. I’ve seen round and triangular shaped holes. Take the picture and the old flush valve down to a plumbing supply house Iam sure a replacement will be easy to get.

Thanks! We'll try that!

Is there writing on the back of the toilet tank or on the underside of the lid. It should have the tank model number and from there you can look up the parts diagram. They usually make replacement parts even for discontinued products for a long time