www.oxygensensors.com. If you are handy with a soldering iron you can purchase the least expensive versions and splice the wires onto the original harnesses. As long as you have a 4 wire sensor you will be OK. The variance in 02 sensors, by location and part number are related to the harness length and connectors.
Just be sure all your connectors are OK first
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HTH,
LarryB