It's possible to access Telegram via Tor (e.g. in-app proxy settings, Orbot or use Anbox in Whonix Workstation).
Signal has the same problems (phone number requirement & even more difficult to access without a phone: https://anarkio.codeberg.page/#/7560cf4a7685/11). Didn't test if Briar/Session work in Whonix yet.
Otherwise there is a (less active) P2P marketplace in Matrix: https://matrix.to/#/#cryptomarketplace:matrix.org