Is there efficient token generation in Black or White?
I cannot think of anything that combos with them for as many iterations as you want. There are a number of effects that create tokens once per turn based on gaining/losing life.

In standard (as both cards you mentioned are standard legal):
Regal Bloodlord
Resplendent Angel

Outside of standard, the best I can find is:
Crested Sunmare
Regna, the Redeemer
Angelic Accord
First Response

In general I think they are quite careful with this effect, and restrict it to happening once per turn specifically to not enable the combo that you're seeking.