U18chan has onion address for years, unfortunately posting is disabled on that port. Neither you can edit a post there.
Even worse, it uses deprecated version 2 of TOR, so it will be inaccessible soon.
However, I was lucky today to hit a TOR exit node that is not on the list yet, so I could get around the first level of u18chan TOR ban and then I could use old familiar way of bypassing second level of u18chan anti-TOR/VPN protection.
So I could update the thread OP finally.