A quick Google search found the Mabuchi Motors website.
Further investigation shows that they appear to make motors that can be used in cordless drills. I found two 12V motors, but how they compare to the old drill motors I have no idea since I was not involved with the drivetrain.
http://www.mabuchi-motor.co.jp/cgi-b...D=rs_540rhshsf
http://www.mabuchi-motor.co.jp/cgi-b..._ID=rs_550pcvc
They also make other motors, which you can look at by browsing around their website.