Those papers were, indeed online when I used them as references a couple of years ago (while doing research on the compositon of the OKC truck bomb). However, like many things in this new medium, they obviously had a limited lifetime. (Webserver filespace is obviously considered to be more valuable and recyclable than printed journals...)
If you are truly interested in pursuing the nitromethane issue, FReepmail me, and I will dig out some current articles for you. Again, apologies for cutting-and-pasting old references without checking...
http://flux.aps.org/meetings/YR97/BAPSSHOCK97/abs/S1700.html