I remember asking a member who was based in mexico, and they said it isn't possible anymore. I couldn't help thinking though that it may be possible, but down to 'what you look like' if you look like a normal everyday person, then you may have problems. whereas if you look a bit ruff around the edges and would be comfortable in a situation like that, willing to pay a bribe. it may still be possible. I don't know this for certain its just a thought i had on the matter. the same with buying most things illegal, if you don't look right in the situation your probably going to get turned away.
what i can say is it seems alot easier in peru, there's a whole street with about 20 vet shops, alot have been named in the PPH as selling it. surely the lava of averages would be in your favour aswell lol