my sons hobby.......

hai frnds....
my son ritvik is 7 yrs old..and very good boy..no remarks at all...wow im really blessed..
he loves to read read read..he live without food but he can't without books...so i thought of give him some hobby..but when we went to india after 3yrs..he really liked all those colorful currency and collected a lot of them atleast one of each variety..he is having nearly 50 coins and 27 varieties of paper currency all collected by himself...so now i want to gift him some thing related to it like a coin collection book where can i find one in store or online...he also collected different us currency canada currency and mexico currency..i love his hobby and want to encourage him so please suggest for his summer gift.....
thankyou friends