Here's a link to the acoustic tuners at Stewmac;
http://www.stewmac.com/Hardware_and_...Solid_Peghead/
I bought 18:1 Grover Rotomatics late last year for a project and do NOT recommend them, too much slop in the gearing so I would agree with Tony Burns and suggest Gotoh or Schaller if you can find them to match the existing holes.
Each the Stewmac tuners have specifcations/measurements also on the page.