Habtom - 10:17 pm on Jan 3, 2012 (gmt 0)

I think helping customers locate products on other websites/stores is just a waste of time. Customer loyalty is not as important as it used to be. I would go with this:

"Oh that's terrible, but sorry, we don't sell that product. We do have these (link) that are (less expensive, better product, define value) if you'd like to have a look. Best of luck in resolving your problem, thank you for shopping with (companyname.)"