Mech relay with pcb socket: Both rated >=240V/15A contact

A mechanical relay with pcb socket. Both socket and relay must be rated for: 12V or less coil; 240V/15A or greater contact; SPST-NC (1form A); 4KVAC or greater isolation

Ronald, Welcome to the Digi-Key TechForum.
A possible match for the relay is
, which is a 12V coil, SPDT, and rated for 15A/250VAC. With the SPDT, you will have both the NO and NC contacts. The through hole socket for this relay is Z792-ND.
Looks like this can only withstand 2000V. I do not see a match to a 4000V isolation.

If you absolutely need that much isolation, there are DC-DC converters that can provide it. You could use one of them to drive the coil.