How to run a 0.05A fan with a 10A source?
You just connect the fan in parallel with the LED, and it will draw 0.05A.  You don't have to do anything to limit the current - the fan does that for itself.

Edit: If your supply is 10V, it would be easiest to just connect the fan to the 10V supply.  It's close enough that the fan should run fine.