Jimm 8/5/2011The Bank 2, Sensor 1 (B2S1) is located on the 4-5-6 cylinder head exhaust manifold downpipe - just ahead of the catalytic converter. The Bank 2, Sensor 2 would on the same pipe just downstream (aft) of the converter.
Try the many on-line auto parts sources, such as; www.RockAuto.com or www.autopartswarehouse.com for the specific O2 sensor. They (Rock Auto) list the O2 sensor from; Denso, Beck Arnley, Bosch, and Standard for around $34.00. They are not difficult to replace - try the 'How-To-Guides' feature on this website for details - including photos.