only muslim factions can recruit them...

have you checked your tech tree guide? it is accurate for ghazi's I believe. To save you the trouble though, (not sure why I would), I'll look myself...

you need a mosque and a swordsmith....
Which is available after at only the 2nd tech level... not at all hard to find.

And if you're of a mind to keep your stacks full, you wont use them at all, (because they die extremely quickly)...

On the plus side they're cheap and they'll add some punch early.