i remoted for a month without getting one book, and now i got 4 in a timespan of 1.5 weeks.
Its a rare drop.
A hint: if training at oslya, borrow a alchemy book1 from someone, or buy one, and keep it in your inventory all the time. that way, even if your inventory is full, you will get the books.
same goes for the wolves, as both raptors and wolves drop a whole bunch of items.