Mathlete.. i had exactly the same problems!
I don't think there are any posters of Andy.. ATP don't produce them and the Tennis Warehouse only have posters of top 20 players..
I'm doing a talk on Murray for my english GCSE.. and i have to use photos! Problem is.. is that the hall, where i'll be speaking is quite big.. so my photos have to be big so everyone can see! ..anyway since my printer is rubbish - ive used the colour printer at school - which does proffesional graph printing..
Anyway once i get the talk over and done with.. those photos will be going on my wall!
Maybe you could print A4 size photos... ?