You can still get new Wii USB sensor bars on Amazon. In the States, they are around $10.
https://www.amazon.com/Sensor-Replacement-Infrared-Nintendo-Console/dp/B09X9SRW72

They are really cheap on AliExpress too.
https://www.aliexpress.us/item/3256801232607668.html

I've been using the same one on different PCs for over 10 years.