I too have not had success with fish that are actually spawning. When I do see groups spawning, there are generally some individuals around the perimeter that can be caught. Generally they are smaller males and its hard to cast to them when you can see a big fat female a few yards away. This is especially true earlier in the spawn.
I’ve fished some areas where the fish were spawning so much your fly had eggs on it when you brought it back. Moving to the edge of the flat i found some receptive fish.