If the magnets are mounted in an aluminum fan, you can use Acetone to help get them out. If it has a solid back, you will need to make a hole back there which in most cases it is easier and safer to just get a new fan. If parts are not available anymore, I would suggest not trying to get it flying as a daily flier. Keep it as more of a casual flier. As for where to get the magnets to check the ones in the helicopter, you can use any magnet that has a defined north and south pole. Fridge magnets are not useful here in most cases. You can order small magnets on ebay all day long. You don't need a large one, just try to find the same size you already have.