Just about any dealer can source a Tank...check the Watch Expert section and also the dealers websites. I bought a Cartier from Andrew (Trusty) about a year ago. For CONUS only check with WBK and his watches, Asian movements but lower prices. Also keep an eye out in the member sales section.
Watchsilix has a great cheap Tank if you're looking for quartz. Very accurate and a great watch. And you can't beat the price (I paid about $45 for mine).