I'm not saying that's not true but I find it hard to believe.
Let's say a car company goes bankrupt? How will they be "required" to produce parts. Moreover, how would the US govt. enforce this law on a manufacturer outside of the US?
As I recall, BMW had to make a very big deal about part availability when they launched their limited run of Z8's. That leads me to believe that there isn't a law.
Either way, if someone could find the truth, I'm intrigued.
EDIT - one afterthought. "Producing" parts and making them readily available isn't really the same thing. I'm assuming (and you know what that leads to) that the original poster is worried about finding readily available parts. My thought is that should be a minor concern. It's already harder to get parts for the NSX than it is a Civic and Honda/Acura didn't sell that many over 15-years (BMW probably sells more 3 series in a month!) so it's likely to get harder to find parts. Wouldn't and didn't disuade me but caveat emptor.