Welcome back! Either here on NP, Sedo or GoDaddy. You could also try Uniregistry, Epik, NameSilo, or any of the other platforms.
There are more of these, like AlpNames, too. However, these registrars' marketplaces are much smaller and limited, for example: Namesilo only for domains registered with them. Same thing with some others....You could also try Uniregistry, Epik, NameSilo, or any of the other platforms.