I wanted to share in case someone else comes here searching.  My Olympia SG1 was missing the ball bearing and spring inside the line space indicator causing it to drift back and forth.  Using the repair manual (purchased from T. Munk) to find the spring and ball bearing part listings, I purchased the closest match I could find from McMaster-Carr.  Working great so far.
--316 Stainless Steel Corrosion-Resistant Compression Springs, 10 mm Long, 2.5 mm OD, 1.9 mm ID
--Hard Wear-Resistant 52100 Alloy Steel Balls, 3 mm Diameter