I recently needed to extract a TTF version of a Mac font suitcase and after trying a bunch of different methods, I found a tool called Resource Finagler.app. It is available from this page on StackOverflow:

Using OS 9 resource fork fonts in CSS

Basically, you open the font suitcase, find the sfnt part, and drag it out to your Desktop and you will have a TTF file ready to use. Here is a screenshot of me dragging the sfnt part out of Resource Finagler.