You can try:
http://www.onda-pet.com.ar/
Looks like they at least have carried it in the past. Giving you a fish is one thing - better I teach you how to fish ;-)
Here's the search technique I used, which has a few good tricks I have found over time here:
1. Search the word you want to translate in wikipedia, then on the left column look for the article in espanol. This is often *much* more accurate than trying to find a word on google translate.
In this case we get
http://es.wikipedia.org/wiki/Nepeta_cataria. There are a number of spanish terms, menta de gato, menta gatuna, albahaca de gatos, gatera, gataria y nébeda
2. Mercadolibre's search engine really sucks, so form your search words into a google search like so:
("menta de gato" OR "menta gatuna" OR "albahaca de gatos" OR gatera) site:articulo.mercadolibre.com.ar
You can use search tools/ time to get more recent publications, but in this case there weren't any very recent ads published.
3. Go to the vendors one by one. Look for a business name in the description. If there isn't one, click their reputation bar, then click the "Más datos del vendedor" link. If they are a regular seller, they will usually put their business name or some ID that you can google and find their contact information.
Good luck, and remember to tell those kitties to practice moderation!
