As a brewer, one of the things you tend to do, is just read cards. All the time. Just make queries on Gatherer or MagicCards.info, read through the cards and you’ll get ideas. Especially, when you are loose on your queries.
Like this time. I was looking through warriors to see if I had missed any for my BR Warriors. I just forgot to limit the colors, so I ended up going through all the warriors, and found a couple of good ones.