There are 2 other ways not mentioned, the best way is to advertise at other poultry shows, you should find them on line contact the show organiser and ask if they can assist either with a flyer you could email or similar (you may offer them/ they may ask for a favour in return but i guess that's what its all about!)
Second is the poultry club of Great Britain has its own website and sends out news letters - (not sure if the next one will be to late) Almost all serious exhibitors are a member of this and the various breed clubs connected to it. You may find people will travel from further afield
Also if your show reaches specific numbers /size/ classes if can be given various different PCGB designation of status ( prob one for the future:0))