It is used, yes, got it in an eBay auction for a touch over £460. There's a bit of information over on Dyxum about this lens, and one other review I have found on Pentax mount...
http://pentaxlenstest.blogspot.com/2010/03/tamron-sp-30028-if-af.html
There really isn't much available to read about this lens, it was only made for the Alpha and Pentax mounts.
EDIT: Update, found one over at DP Review that someone seems to be willing to sell, cosmetic condition isn't great, but this lens is built like a tank, glass looks okay from the pics and the mount looks clean too. It still has the original drop in filter.
http://forums.dpreview.com/forums/readflat.asp?forum=1056&thread=38985234http://forums.dpreview.com/forums/readflat.asp?forum=1056&thread=38985234