In Europe (well, at least in several countries) we can hardly find catnip, and when we find some, the package is ridiculously small for a very high price

In France it's not very common to give catnip to our kitties. Poor guys It is with PT that I realized how common it was in Canada and US!

Recently, my partner went to Canada for his work and I gave him the mission to find good catnip. He brought two brands, one was the "Cosmic" catnip, and I don't remember for the other one (I am not at home to check). I cannot give you a comparison with other brands, but these ones have been largely cat approved

Here is a link for the Cosmic catnip:
http://www.cosmicpet.com/detail.asp?col=3&id=1

Your vet could go to Canada, let's say for holidays, and bring one or too suitcases of catnip