I always sample foodstuff before buying in bulk. In the case of salted duck eggs, the yolk has to be oily. I’ve taken notes on where to find these in Bulacan, Pampanga, Manila etc. In Laguna, I think the most consistent is from Victoria Laguna. I’ve been buying their salted eggs for more than a year now. I buy these from their outlet in Calamba. If you’re familiar wth the new Calamba City hall and the Rizal Monument. Going towards Manila you’ll pass by Shell Bacnotan. The outlet is near the Gas station. You can also visit their blog or facebook account.
Most of us serve salted eggs with tomatoes and onions, or part of the bibingka. I tried using the yolk with olive oil and garlic as a pasta sauce. My friend Chef Johann Santos suggest that one should soak the eggs in warm water before serving to activate the oils of the egg.