I know this thread is very old but just to update for future searches.
You can buy the micro ball bearing of 1.5 mm and 2mm diameter which are used in various old pentax lenses aperture ring at Amazon.com
100 2mm Chrome steel bearing balls: Precision Balls: Amazon.com: Industrial & Scientific Generic 304 Stainless Steel 1.5mm G100 Loose Bearing Balls (Pack of 100): Amazon.com: Industrial & Scientific
Now only if I can find a place to buy those tiny springs on which these balls sits.
Hope this helps someone.
Happy fixing.