I can't think of any store-bought dead ones.. The only fish I can think of that could be fed whole to a really small baby are guppies.
Lora
3.0 T. sirtalis sirtalis, 1.1 T. cyrtopsis ocellatus, 1.0 L. caerulea, 0.1 C. cranwelli, 0.1 T. carolina, 0.1 P. regius, 0.1 G. rosea, 0.0.1 B. smithi, 0.1 H. carolinensis
You could use pond smelt if available (Hypomesus olidus). I've found them smaller and they're on the safe lists. Just chop up the whole fish into bite sized pieces if too big. I find a pair of scissors works great and is very fast if they're still frozen or partly frozen. Thawed out will be messy.
The sanfrancisco brand silver sides I have recently purchased have been pretty small- minnow sized rather than sardine sized. If that is still too big, slice them crosswise while still frozen.
my young butlers will steal fish with heads bigger than their heads from the bigger ones and wolf them greedily. No regurgitations so far.