Your dad can can go to any gun shop and "feel" a large variety of handguns. That will eliminate many choices without even firing one just by feel alone (i.e. too large, too small, too thick, too heavy, etc). After he has narrowed down the choices by feel (in my opinion, this is the most important factor anyway), it will be easier to track down a gun shop that has a rental unit, or find out if anyone on INGO has the same model they would be willing to let him try out (you will supply the ammo, of course).