I own a Dean Pace also (the few, the proud...

). Was the bass on the tripod stand when it was knocked over? That must've been some shot to make it fall like that...
Anyhow, the tuners seem to be pretty standard (cheap) variety, like the kind you find on a lot of MIM Fenders, Squiers, etc. Something like this would work well:
http://www.allparts.com/store/tuning...03,Product.asp
Regardless of what you end up going with, make sure you order the correct tuner - meaning, if the key that broke was for the E or A strings, you'd need a right handed tuning key (or left handed for the D or G string)
My Pace came with the case included. You might want to shoot Dean an e-mail directly, or go to your local Dean dealer & they might be able to get one for you.
As far as the preamp issue goes, I remembered seeing this thread in the 'Electric Upright' section of the Double Bass forum. You'll see that it doesn't really have a happy ending, though...
Dean Pace Bass Electronics Upgrade
You could consider using an outboard pre. I use a Fishman Pro-EQ Platinum Bass Preamp for mine & it works great.
Good luck!
