Occasional Instruction in own airplane

Hello,

I'm a CFI, and am considering buying a Cherokee, mostly for personal
use. I would like to be able to offer occasional flight instruction in
that plane (less than 50 hours per year). This would consist mostly of
BFRs and intro flights. I recall seeing that insurance for such
occasional instruction was offered somewhere, but I can't seem to find
it. I don't want to pay an extra $2000 for such coverage tho. Is
anyone else doing this, and if so where did you obtain the appropriate
insurance coverage?

Thanks,

Chris