i have a masterball but soory im not giving it away fro free.
little tip for giratina and mesprit
for giratina, take a pokemon with status effecting moves like poison powder, sleep powder and a pokemon that is effective against ghost/dragon pokemon, beat it up untill its in the reds and start throwing ultraballs, it will take a while but it worked for me, oh and dont forget to save before you battle him just incase you killhem or he kills you.
now for mesprit, its a shame i didnt find out this technique before i got fed up and used my only masterball at the time, for this pokemon i recomend a gengar with the moves mean look which provents the pokemon for fleeing, hypnotise which puts it to sleep and 2 power moves of your choice. when you find it use eman look and start using moves, when its a low heatlth once again throw ultra balls and you should catch it.