I had heard that is was all wiped out when the feds were providing the mex govt with paraquat and helicopters to spray all the fields they could find. However I think I have seen it at some of the seedbanks so it may still be out there somewhere. For you youngsters, in the late 60's and early 70's the feds had a program of spraying mexican and columbian pot fields with a defoliant called paraquat. Nasty stuff that stayed on the plants and could (and probably did) have some very unhealthy effects on the end users who smoked the weed. It's use has since been banned in the US.

http://www.bt.cdc.gov/agent/paraquat/basics/facts.asp
http://www.drkoop.com/ency/93/001085.html