If you're willing to do a little bit of modding, check out Energon OP-3
http://www.tfu.info/2004/Autobot/Opt...timusprime.htm
And harvest its drill bit. More detailed than the standard corkscrew style.
Or look into Cybertron Menasor
http://www.tfu.info/2006/Decepticon/Menasor/menasor.htm
He's got two drill arms, one becomes a claw.
Lego Power Miners, Rock Raiders, Mars Mission, City-Construction, and City-Mining sets should provide some nice drills and other construction accessories you may want to use.
edit:
And keep an eye out in dollar stores for cheap toys that may contain drills.
edit 2: Also check out the Thunderbirds MOLE models. Not sure about scale though. And for some added kick to Hercules, harvest Cybertron Metroplex's weapon and Cybertron Quickmix's arm (mod into a gun).
R.i.D. Build team (or Universe Devastator if you want to paint less) can give you some nice smaller accessories like a crane arm that turns into a sniper rifle, a dump truck bucket that turns into a shield (or folds out into a barricade), and a backhoe arm and shovel that turns into... some kind of claw?
Plus check out Smashmaster Seismus for a hammer mini-con. Also look into Power Core Combiner Mini-Con Throttler, Prime Arms Micron Balo, and the Armada Destruction/Road Wrecker Mini-Con team.
There's a number of other Mini-Cons and Microns that have to do with construction that you could harvest.
edit 3:
Power Core Combiner Steamhammer comes with some construction based drones, one has a smaller arm with a smaller drill on it.
Or Beast Wars 2 Galvatron's neck/drill might work well for you
http://www.tfu.info/1998/Destron/Gal.../galvatron.htm
