The current iteration of the Tamron mail-in rebates are good until June 30, 2012. You can find them nicely organized at B&H Photo. They are available in Canon, Nikon, Alpha Sony Minolta, and Pentax K-mount. Please note these are mail-in rebates, which means you have to fill forms, cut bar codes, make copies of your submission, submit, wait, receive check (or follow up if there is something wrong), and deposit the check.
It would be nice if they switched to online rebate submission like the Staples Easy Rebates. Online rebates are better for all parties involved, faster submission, easier verification, reduced fraud, happier customers.