anyone know where it can be purchased or how I can acheive that color on a cake? I have searched the net and can only find gold or silver.
Somehow, I don't think you're going to find it.
The only reason why pure gold leaf is edible (albeit awfully expensive to be putting through your digestive system) is because gold is almost completely inert (and certainly about as bio-inert a metal as you're likely to find).
Rose gold is an alloy of (typically) 25% copper, 75% gold. Copper isn't so bio-inert.
I've had some success painting rose gold by mixing a little dry pink dust into dry gold dust, then liquifying it into paint. Rose gold leaf isn't edible, but can be used IF you put it on fondant and remove the fondant before slicing the cake for services. I insert a clause in the client's contract requiring them to assume the responsibility of removing any inedible elements like this from the cake before service.