I found this update in FAQ on Paul Graham website
(http://www.paulgraham.com/faq.html). Looks like he is going to put it
on line.
Where can I get a copy of On Lisp?
Unfortunately it is out of print. I've heard there are some copies
left at amazon.co.uk, but they are not likely to last long. If you
like I can put you on this page, which has led to some people getting
copies. Copies also sometimes come up for sale at eBay.
I got the rights back from the publishers and plan to put it online,
but at the moment I'm too busy with Arc.