The First Aid Expert Book is found off of a "Reagent Supplier" in Arathi Highlands, Stromguarde Keep.
This area, though scary, can be reached easily even by lower levels, by entering the courtyard of the keep, skirting the wall on the right. You will come to a T junction, facing a keep entrance, at which you will turn right. Be cautious, there are stealthing rogue mobs there, generally if you see others, you'll be fine.
Go directly ahead of you once you have turned right, and you will see Green named mobs, looking like human knights. Go into their courtyard, turn right again, and once more. You will see a nifty "garden" looking area, turn right as soon as you have cleared the trellace. You will see the vendor, who sells the book for 1 gold, as well as two other recipes for a few silver (20, no more than 50).
You can acquire this book at any time, but you will not be able to use it until you have reached 100 FA.
