The Twilight Sparkle Crystal Heart Spell, Welcome to Equestria, and MEet the Ponies books have all been officially released. Chances are you can find them at most general stores (Target, ect) though we haven't had any specifics outside of these that appear to be from Safeway.
Anyway, happy hunting! Under the Sparkling Sea hasn't popped up yet, but they don't seem to keen on release dates with these, so it might be floating around somewhere.
And in other news, A Rainbow Dash book titled "The Daring Do Double Dare" was included in this completely random flier (found above) sent over by Brony250. I guess we can expect one for each pony at this rate?
