Morning Jaime, well in the clear light of day I've had a look and I'm sorry I don't have the decals you need ,my finished FAA Seafire is the same as yours so the decals you want are used and the first one that was reincarnated as USS Bunkerhill also started out as the same aircraft and so they were used as well, my only advice is to buy a decal sheet of letters and numbers just make sure they are the correct size I think the size you want is about 6mm,they may not be the same font but no one will know (or care) as long as they match so you will have to carefully scratch off or paint out the remaining letter P, don't think of it as a waste of money as you will probably use them again some time ,they are handy to have in your decal bank,alternatively you could just remove the remaining P and leave them out until you get round to attempting another Airfix Seafire in the other version,if you dare!, it could be a rights of passage kind of thing "Your not a scale modeller till you've built an Airfix Seafire young man now bugger off",we could look down our noses at lesser modellers who haven't finished one (LOL)!
N.
P.S. anything you build after this will be a walk in the park.