Is it safe to let my cat eat catnip everyday? where can I buy it?

Yes you can give your cat nip everyday but in doing so he may not get as excited if he's exposed to it a lot.  I read one article where the cat began to not like it.  I guess it's the same if you ate something every day and then had a distaste for it.  So I would only give your cat catnip once maybe twice a week.  But I think once a week is the best.  I have chosen a few selections for you below.  You may want to go to Ebay as well because when I was searching before I found people that made these cute little cat nip toys with organic cat nip inside.  If you don't see any right a way, keep your eye on them because they're cute.  You could also grow your own. 

Hope this helps.