They usually use a round bit of metal with a cut ... something like in the picture below. You're supposed to insert a small chisel like tip screwdriver in that cut and twist gently to stretch it, making the hole larger - the metal ring sits inside a groove in the metal axle. As you stretch the ring and make hole wider you should be able to lift the ring up and then you can take out the whole blade and axle out and lubricate it.
But anyway... these fans seem to be available everywhere if you google for the part number, you could just buy new ones. And you could probably also just measure the distance between the mounting holes and find other fans that would work.