What's funny is you don't even really need the bar. It was officially called the sensor bar, but it's a misnomer because the sensors are in the Wiimotes. The bar is just a pair of IR emitters.

Anything that emits light on the infrared spectrum can be used instead. One "hack" is to use two lit candles spaced a bit apart. Around the holidays, you can just use a Christmas tree. Or on a good day, you can even sometimes use this magical thing called the sun (though its position won't be static).

You could also buy two IR LEDs and stick them in a 3D printed frame for a DIY solution (or just tape them to a stick). It's definitely the least critical component of a Wii to have to replace.