Thomas Paine to George Washington: https://founders.archives.gov/documents/Washington/05-20-02-...
Another good source would be the newspapers from the time: the Philadelphia Aurora had a good for the circulation of the time, was a "respected" paper (as far as that went then), and has lots of very nasty things to say about Washington during his presidency. It (and a selection of other papers) will give you a vastly better idea of the political climate than just about anything else you can get.
You can see a wide swath of people who knew Washington thought very poorly of him, especially militarily.
> I've read the biographies of most of the founding fathers, and in none of them does anyone strike out against the great man himself.
Reading biographies is better than nothing, but they usually have an agenda. Not that say, Paine or Rush didn't, but we're talking about how Washington was view among his contemporaries and how the speech was received and understood at the time. Later works are going to be clouded with different agendas, particularly the mythologization I mentioned.
