Lots of broken spokes on one bike, with different wheels
Are your brakes properly aligned? If they're off-center, every time you brake you'll generate a lateral force on the wheel that spokes absolutely hate.
How do you store your bicycles? Do they live in the garage or in the living room? If you live near the beach, the salt can cause corrosion and weaken the components.
Like the comments said, check the fork alignment. Since you stated that you had a wheel lying around that had never been a problem before mounting it on this particular bike, it leads me to think that there is something wrong with the current bike.