There’s a number of tiny prey items that can be easily cultured but ideally these would have been started way in advance of them morphing.
Fruit flies have the fastest turn around (D.melanogaster are the smallest commercial variety) but are not a complete food and will require dusting with a vitamin supplement. Other good cultures to have on the go include lesser waxworms, woodlice, spring tails and mealworms. I believe some keepers in the US use blackworms in a shallow dish of water to feed morphs. Another option is to chop small earthworms into bite size pieces that still wriggle enough to attract their attention.
Mark