If you do lose the ball, this place has a huge variety of them...
http://www.vxb.com/ballbearings.html...FSA4hgods24arQ

Other sources are industrial supply distributors:

http://www.mcmaster.com/
pg 3566 "Metric Stainless Steel Balls"

a very good source for all sorts of stuff...

--
Nicholas O. Lindan
Cleveland Engineering Design, LLC
Cleveland, Ohio 44121