If you know there’s pods in your system then pulling some rock rubble or chaeto and culturing it should be able to start a culture.
I did this once to see how it’d work - just took a small stone from the sump (I keep rubble in there) and added it to a clean culture vessel. Next day a flashlight showed a bunch of pods swimming around, so must have been carried in on the stone. Figured as the culture was already “contaminated” may as well leave the piece in there to help with ammonia control. Culture is going well.
One reason not to do this is that it risks contamination of the culture with other life from the tank that may take over or cause problems, but at the DIY level I’m not sure that’s really as big an issue as it would be if you were doing this commercially