I don't think ISBN numbers are any good for ebooks, which I interpret to mean electronic works which can be downloaded. The clear implication is that he wants them for free which is why I suggested the author since he might actually have done such a thing.Once you get the ISBN numbers of the books your interested in, visit http://www.half.com where you can purchase books inexpensively.
I've never come across a cookbook perse. The best free on-line resource I have come across is http://www.cmosvlsi.com/where can i find an ebook of all cmos/ttl/linear cookbook?
do you have any links ?