I've never seen cultures - you can get pupae or spikes at mantis place - the spikes are the larva which will turn into pupae if you leave them out of the fridge for a couple of days - the pupae hatch into flies a couple of days after that - depending on the time of year -
I get mine from mantisplace.com- I have 3 chameleons so I get 100 pupae and 500 spikes usually - the pupae I split into 4 or 5 of containers and put one on the top of the cage and one at house temp and the others in the fridge so they hatch at different times - the hatch rate goes down with time but an order will usually last about two months -mixed with other feeders - I've had good and bad hatch rates with different orders - different times of the year -