Does anyone know where I can buy a radiometer - other than online?

Question

you know that glass ball thing that spins inside when the light hits it

Answer 1

You can get one at an educational store or Discovery Channel store in a
mall. I've also seen a few in gift shops, some toy stores may also carry
this. I'm not sure where you live but I've seen a lot in my area in PA.

Answer 2

Many science museums and planetariums sell them. Also check out mail order houses like Edmunds Scientific where you can order by phone, catalog, or online.(Radiometer $12+) They've been in business for a very long time.