You can harvest this in Giddeus. It's a fairly common item to harvest from my own harvesting experience, but it's probably easier and more frequent with field gear.
I agree with Ryuchan of Unicorn. Harvesting in Giddeus is a great way to find plenty of Red moko grass. This gave me the gil to make it to level 60+ (66) then I moved onto another farming. This is a common seller on Siren too, but price fluxuates very often. It says average sales, but in my own experiance I've put up 7 stacks and all sold within the day. Good luck on farming everyone! :D