I ran into the same lack of 4" spinner problem when finishing my TF p-51. As far as I can tell (and LHS sort of agrees) the major manufacturers don't offer 4" spinners in plastic (biggest we found was a 3-1/4). I ended up with a Dave Brown 4" aluminum spinner/prob adaptor for about $40. You could also order a TF ARF replacement spinner from Tower, but it only comes in a red/yellow color combo. HobbyPeople has (or had) a Magnum 4" aluminum spinner listed in their clearance items a couple of weeks ago.