There are some dressblooms that you can get without paying, though they are limited so I'd save them for only girls you want to RG. First, there are 3 that you can get from the Life Crystal Shop for 2000 each. Seems like a lot, but you can farm a lot of Life Crystals from Ultimate maps when you can do those.
In my entire time of playing I have accumulated a total of 6 gold dressblooms, so there must be some quests that give them as well. We do get Sealstones every once in a while and if you aren't desperate for any waifus, you can buy a dupe of the girl you want to RG.