Basic electromagnet question

What are some of the better places to buy electromagnets from?

Is there a way to calculate the repulsion lifting force that they have? I've noticed that a lot of data sheets will list lifting force, and a few list pulling force, but haven't seen any that list repulsion/distance. If you have 2 of the same electromagnets next to each other, and two properly oriented permanent magnets (as opposed to 1 electromagnet and 1 properly oriented permanent magnet) does the pull force double and the push force double?

Thanks for reading!