Do e.g. CMD+SHIFT+G
and then
Code:
~/Library/Application\ Support/REAPER/Osc
... short for
Code:
/Users/[YOURNAME]/Library/Application\ Support/REAPER/Osc
(Tip: Apple has hidden ~/Library from plain view, starting with Lion. Drag the folder to the sidebar of Finder to create a shortcut under Favorites, so that you can easily find it next time. )