famotidine sources

I need to give a cat 5mg. of Famotidine twice a day. Currently, I can only get the 20 mg. size pill. Is there a source where I can buy the Famotidine in the 5 mg. size tab? Or, if not 5 mg. size, 10 mg. whereby the pill can be spit in half rather than quarters? Quartering the pill -- the pill quarters in the bottle, break down and crumble so I don't know how much the cat is getting in her dose.