The Stewart-MacDonald Catalog on page 58 has an internal mic. It's made by GHS and is called a 'Mini-Flex Guitar Mic System. It retails(out of the Stew-Mac)for 99.50/US. The part # is 3382. It's got a special cable(# 3388) for 29.00/US. Here's what the copy says:

"'Mini-Flex' is a miniture low-impedence mic mounted on a flexible gooseneck, with an integral 1/4" endpin jack. This design suspends the mic inside the guitar without contacting the soundboard or altering the instruments acoustics. The mic can then be positioned for best sound. Instructions and battery included. Cable must be ordered separately."

This is what I am going to purchase for my autoharp as I don't want to use a piezo or a magnetic. It would probably adapt easily for a hurdy-gurdy. There's no doubt, you'll have to eq the daylights out of it ahead of the system, but I'll bet it'll sound very natural. Stew-Mac has a website: www.stewmac.com You can order online or use the '800' number. Good luck!