What are you using to get the depth with the cutter?
Hole saws are a relatively easy item to get hold of.
What are you using as an extension?
I have not done the baffle-ectomy but I was an electrician for many years and used drill motors with very long extension, sometimes two at a time made by Milwaukee for the large boring bits (2-3-4"dia bits) I suspect these or something like them would work with a carbide hole saw.
Check with an electrical construction supply.