The item you are looking for is more properly called a "slide chart" rather than a slide rule. I would suggest looking on ebay for a geometric tolerancing slide chart under the "slide rules". They pop up often, and many of us mechaical engineers still keep one around, even though we have transitioned to CAD systems (I use Pro-E at Sun Microsystems).
As a side note, I am also the curator (and webmaster) of the International Slide Rule Museum www.sliderulemuseum.com as well as the webmaster of the Oughtred Society www.oughtred.org
Take time to visit, and if you want to donate your dad's slide rule (or your's) to the museum, send me your (or your dad's) picture with it and what it was used for.
