I have the Sigma 18-200 lens but someone was telling me he was waiting for the Tamron 18-250mm....well here it is ....! Hopefully once you buy it can give a review and comparison between the sigma 18-200 and the tamron 18-250!
http://vshopusa.vpost.com.sg/aom/shop.php?c=15&n=493964&k=pentax&s=sr&p=11&x=Electronics_pentax
http://vshopusa.vpost.com.sg/aom/shop.php?c=15&n=493964&k=pentax&s=sr&p=11&x=Electronics_pentax