With your 4mm shaft you have alot of props to choose from.
I hade very limited sucess with the sab props.
The academy and kyosho props are a lot better, I have yet to try the Graupners.
Now if you have enough shaft protruding from the stuff tube then you can fit a drive dog then the prop slides on and last goes the prop nut. Another alternative is to use silicone fuel hose instead of a prop nut. I have only lost one prop with the method and that was when the little hydro hit a log, it tore the prop off and bent the shaft[X(]
Hobby city do have kyosho props, HPM in Browns Bay will post stuff out. I live in Birkdale and still get them to post me stuff. The other shop I use is Ace hobby in Birkenhead.
You can use 3/16" octura props with an alloy or brass sleeve to step it down to 4mm. I do
I also have bored 1/8' props out to 4mm
Now that I am building my own shafts I make them to suit the intended prop.