BestOfLemmy

They are available at many retail outlets, though not cheap if you want decent quality. I got a UNI-T brand one and have been fairly pleased with it, though I think Flir is more common.

https://thermal.uni-trend.com/

I also have a coworker who recommends a thermal monocular for longer ranges, though I can't particularly comment on that. He uses his to watch animals on his property. I've heard they're commonly used for hunting.