Second, it's catching on in the Netherlands through the underground. All hackerspaces have their own supply line, either through their own import, or through other channels. There are now several wholesalers who sell it, and I'm starting to see it in small cafe's as well.
I've also heard that there is a cocktailbar in Amsterdam which uses Club Mate in some of their cocktails.
I'm an Argentine who enjoys mate. While in Germany I tried a Club Mate and found it disgusting. It may be an acquired taste though, much as plain mate is, and I'd gladly give it a second chance if I could get my hands on some.
It's more difficult to find than Club Mate (it's a local brew from Hamburg). Depending on your taste, it contains much less sugar than Club Mate and feels more 'herbal', I prefer this.
If you're looking for places to buy, Matekarte[1] provides a nice map detailing who sells what and the latest status (in stock, only few left, out of stock). Unfortunately, it appears to only be available in german.
I only know two places to get it in California. One, The Fizzary on Haight in SF, the other Galcos Old World Grocery in Pasadena although my impression of Galcos is they aren't going to keep stocking it.
It's one of many drinks that seem like they could do well with the right marketing and distribution.
These drinks really have very little to do with the taste/experience of the traditional S. American mate though...
I imagine it would catch on in a far bigger way, but no one has heard of it. It was only through a HN article on SoundCloud's Berlin offices that we decided to try some.