What Propeller for Apache 24

Hi guys, A while ago I bought and Apache 24 for my 12 year old grandson. We
replaced the stock motor with a Graupner Speed 600 but left the stock prop. I
believe we need a bigger prop or more pitch. What propeller should I get that
fits on the stock shaft. Thanks for any help.
Norman2

I have been asking this same thing but with no luck!