[CSS21] os/2 and hhea tables

I'm trying to better understand/predict font-size versus content area for various fonts, and it seems I need a better understanding of font metrics (for example, how a font's glyphs relate to the font's em square). From the CSS2.1 spec (section 10.8.1):

"Note. It is recommended that implementations that use OpenType or TrueType fonts use the metrics "sTypoAscender" and "sTypoDescender" from the font's OS/2 table for A and D (after scaling to the current element's font size). In the absence of these metrics, the "Ascent" and "Descent" metrics from the HHEA table should be used."

I'm usually pretty good at "Googling", but in this case I haven't been able to locate OS/2 and HHEA tables for particular fonts. I'll I've found is general information explaining what the variables such as sTypoAscender mean. Can someone please point me in the right direction in terms of how to find *specific* font metric information for a given font?

Thank you