Hi Tony
If you were to stick to types used by the RN with planing hulls, WWII and post-war, at 1/24th scale (to take advantage of the fittings, weapons and plans already available) and end up with a model of approximately 3ft long you would probably need to choose from the following;
BPB MGB/MTB 71.5FT
BPB MGB 70FT
ELCO 70FT MTB
Higgins 78.5FT MTB
Vosper MTB 70FT
Vosper MTB 72.5FT
Vosper MTB 73FT
Vosper MTB 102
Thornycroft MTB
JS White 73FT MTB
Gay class FPB
Dark class FPB
Vosper 74.5FT MTB 538
Saro 75FT MTB 539
Regards, Christian.