I haven't really heard of character cards that drop on specific conditions, I thought just the fish card was like that. You'll just have to keep playing to unlock most cards, it seems that you're more likely to get cards of the character you played as in the match so just keep playing as Reimu for her card? Arcade mode ( or whatever it's called, the marathon battle mode ) gives a ton of cards at the end, though doing that many battles outside of it would probably yield the same amount or so, I'm not sure.
It took me forever to get all the cards for my main, and I might still be missing a few spellcard attacks. Just keep playing and, with a bit of luck, you'll be bound to get the card you're looking for.
( Anyone feel free to correct me if I'm wrong, I'm basing the drop system mostly out of speculation and quick glances at some sources. )
