I really dont think youll find it less than msrp for awhile outside of amazon. Nintendo always has a tight grip on their bread and butter titles like pokemon, metroid, zelda and mario.
If you pre order from amazon though they have them for 35 with the pokewalker included, a bonus figure and free shipping. Msrp on it is 40 bucks I think so thats about as low its gonna go I would imagine.