Where is Google's file cache on OSX?
OS X stores user caches in ~/Library/Caches. The Library folder is hidden, but you can enter it by going to the Finder, click Go, keep ⌥ pressed and click Library.
You said in the comments that the cache is not easy searchable.
You can also try searching from the command line:
cd ~/Library/Caches/$FOLDER
grep -Rl '%PDF' .
If there is a large binary blob cache file, you can try using a Hex Editor (I like Hex Fiend for OS X). Search for Hex 25 50 44 46 (%PDF), start copying from there and store it in a new file. Good luck!