In Kingdom Hearts 2 how do you get elixirs?

If you defeat certain Heartless, rather than getting a circle-shaped red or blue special orb, which will definitely contain a crystal, gem, shard, or stone, sometimes you get a dark blue orb which is shaped like a mini treasure chest, you can usually get elixirs, but you can only get them occasionally, and not all the time. Failing that, you can buy them or synthesize them from moogles, or just get them from shops.