In that case, we’re in the same boat… I did somehow manage to figure out how to play the Pokemon Tretta Japanese arcade game after a few failed attempts… but for the life of me, I couldn’t even figure out how to get started with the DBZ Heroes arcade.
Cards come either from packs or vending machines. The rarest / most useful cards for the arcade game can be relatively expensive, but bulk cards (that just look cool) are pretty reasonable if you can find them. Last time I checked ebay there were a handful of listings of both packs and loose cards.