You can win Dark Matters in the European Version by overkilling Special Monsters in the Battle Arena. only get 1 or 2 tho but worth it if you are trying to get Ribbon on all your characters.

As for catching 5 of all monsters for 99 dark matters, my advice is only get these if you have no dark matters in your inventory, either use them or wait to collect them after getting these, as it can be annoying to save up a few dark matters then losing them all when you get 99 and having to start over when you add 1 ribbon.