A question for plumbers

[brslk]

I was looking for a way to connect a hand held shower to the bathtub faucet.
Home Despot doesn't have the right fittings and I'm not even sure they exist. I'm sure there's a way but not sure where to get the pieces.
What I'd like to do is to remove the aerator from the end of the tap and attach a diverter to a hose connected to the hand held shower head.
The tap has the regular fine threads on the end once the aerator is removed but I can't find a diverter with the same threads on the input end.
The wife has been using one of those hand held units that slip over the end of the tap but it isn't ideal and rather inconvenient.

My question is, do any of you know where I might obtain such a fitting(s)?