How do I obtain lots of fodder Digimon?

I've seen a lot of guides online say the best way to get extra stats is to use extra Digimon I'm not using from extra converting data and feed them into Digimon I am using. And these guides have a ginormous box filled with tens if not hundreds of extra Digimon to use up. I don't have that many and was curious if there is a fast way to get a lot or if it is extremely time consuming to reach that many extra Digimon?