From what I understand it's all about shooting the pistol to break in in, not the bullet you shoot. I'm told the break in process is all about smoothing out the "rough spots" on all the moving parts. Most any ammo will do that. That's a good suggestion above to use what you can find that's cheap.
Of course you will have to shoot your carry ammo to be sure it reliably shoots and cycles the pistol before you commit to carrying that ammo, but that's another thing.