good on them for proper customer relations! I suspect the real deal [actually Ortho-phosphoric acid] is getting harder to find, but it is still used as a "metal prep" under various brand names
look for one called
OSPHO at paint suppliers or marine supply places - and
here's one [in PA] that has a 5 gallon size, and
one in gallons - what you want is 75-85% acid, usually they'll say to dilute with 2 or 3 parts water .... POR15's Metal Ready is a very dilute phosphoric acid, less than 10% I think meant to not be rinsed off
Bill