Sometimes people find their restorer first; then have that person find the engine…..or they bring them one to restore.
Some of these people do jobs to order; give them an order and they will take it from there. They have spend years building up contacts and resources at the bone-yards out there.
Sometimes you can talk a member into picking up a motor for you and holding on to it…..helps if you locate something across the country and can’t arrange to drive over there right away 🙂