I hope you don't mean you're checking to see right now! You're only a few weeks along if my memory serves me correctly! Anyway i have no idea where to find them. Find a midwife, ask for some. She'll probably hook you up.
Hmmmm....I'm not sure everyone agrees about the nitrizine. I do know you can get a hand lens, collect the fluid as it comes out, and look in the lens for ferning....That would be a better test than the nitrizine paper.
Try googling midwifery supplies....
Or go to www.birthwithlove.com This is where I got my birth kit for my first baby. Lots of good stuff on that site. NAYY.