Hello: It must be my confusion is rubbing off :shock::D. You’re looking for high end residential or a small commercial heater. I’m not sure you’ll get much of a selection in a big box store. A plumbing wholesaler would likely be better at having something in stock. What it really boils down to is what’s available in your Dad’s area. Although there are many sub-brands, AO Smith, Rheem and Bradford White are the major makers of heaters now in the US.
I’d see if wholesalers in his area are willing to sell to the public, or find a local plumber who can help. Or, fix that valve to buy time and order a heater from a Big Box store.