The G, the S, the C all present in different faces but can't find this one...

Since the date is 1908, I seriously doubt you can find an exact digital version.

This is true, the Association was founded in 1908, but the logo could have been created after the fact (I'm hoping!)

From what I see, this is not a logo, but a commemorative coin. That means that most probably they've used something non-digital to do it, even if after 1908.
If you do need to recreate it, I think your best chance is to pick up the most similar typeface you could find (Century?) and customize the needed letters.

(maybe I'll go for the typeface with the most similar Ss, because they're harder to modify)

You can try modifying GOTHAM

http://www.typography.com/fonts/font_overview.php?productLineID=100008