Here's a link to the grip for S95.  http://www.lensmateo.../S95S90grip.php 
From what I've been told and read, the grip helps a lot.  I know there are couple of folks here with the grip. 
 
As for where to buy one, Canon's a got a refurb one for $319.99.  Of course, after shipping and sales tax, it's back up to ~$360, so you're probably better off buying a new one and have one-year warranty (vs. 90-day for a refurb).  I've been looking at it on and off for a while and no one reputable is selling one for less than retail ($399) so I'd just pick a store that has a good return policy. 
 
Are you going to IR the thing?