Great for finding official Olympus (OM System) branded spares.

Since the LI-42B is a "legacy" item, these retailers are your best bet for reliable stock:

They are 100% interchangeable in Olympus Stylus and FE-series cameras. What to Look for in a Replacement

Here is everything you need to know about finding the best power source for your camera. Is the LI-42B still available at Best Buy?

Ensure it is Lithium-Ion (Li-ion) to avoid damaging your camera.