I bought an extra from Otto Frei a couple of years ago.
This may be what you're looking for? $69.US plus shipping.
Genuine Omega Crystal With White Ring PZ5078
063PZ5078 GLASS PLEXI ST RING D34.12 H4.5 Fits Case numbers: 2026, 2915, 2998, 6049, 105.002, 145.002, 145.0002, 11003-2 063PZ5078 GLASS PLEXI ST RING D34.12 H4.5
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