The internet!
Search 'Spitfire' and you will pull up many sites dedicated to this famous aircraft. When I get around to it I purchased the new Tamiya 1/32 kit. I found a picture on a Spitfire site of a bare metal Mk 1 hybrid that flew around Canada in 1946 for public relations visits with a Lancaster bomber. The only modifications I plan are the removal of the weapons & wing blisters.
Every modeling site will have a search feature, do the same there and you probably will find a thread dedicated to the kit you plan on building. 