Any Z-wave dry contact sensor will do. Unfortunately, I was able to find only one other comparable product:
https://www.amazon.com/gp/product/B00B6RZ7MM
This device is a tad more complicated and bulky in comparison to the simple and small Aeon Labs product, but it should work. It’s designed for both input and output, but you can wire it as a dry contact sensor and ignore the output function.
It also requires a 110V power source for the wall plug power supply. You can locate the MIMOLite near the power source and run the pair of wires to the doorbell chime unit. OR…
The MIMOLite does have one potential advantage: it MAY be suitable to wire directly into your doorbell transformer and eliminate the need for magnetic contacts. It can handle up to 16V input, which most analog doorbell systems use. You might be able to locate the MIMO device near the transformer, which is likely next to its own 110V outlet.
Here is a Smartthings user who says he installed it as a doorbell sensor.
Here is an Amazon user who says the same.
https://www.amazon.com/ask/questions/Tx2EYR3YWA4RQFG/ref=ask_ql_ql_al_hza
The Smartthings user shows it wired to the contacts in his doorbell chime unit. I would opt to put in in the attic and wire it to the transformer instead. I haven’t done this myself, so I can’t offer much assurance, but their posts appear credible.
I’m really bummed by Aeon Labs’ decision to discontinue. It’s a great little product that has a lot of uses. That may be the reason third-party sellers have inflated their price to nearly five times the original retail price!