I haven't heard anything that I can substantiate. In the past few years, availability has been a problem. I did read an article in regards to the World Health Organization (WHO) stockpiling Tamiflu due to what they feel will be an empidemic of the Asian (bird) Flu especially in third world countries. But...in saying this I don't want to start a panic and everyone start stockpiling Tamiflu. Roche is working with the WHO to ensure adequate supplies will be available everywhere.
I just read something from a site called e-drug that TamiFlu may not be effective against Bird Flu, but they seem to be more concerned about that in the Third World countries. You shoud subscribe to this site. It's like a world forum; you get daily emails from all over the world about different issues regarding World Health. Though some of the stuff is tedious, they come up with some really interesting stuff from time to time. And, of course, it's free.