Replacements may be available, but Omega has not made gold filled or capped crowns since the late 60's
All are now gold plated.
Do a Google search on the case reference numbers and try and find a 2 or 3 with the same crown style. This will show you he style needed
Check shows a slim profile, but you can use whatever you like as long as it fits the case tube and stem if needed
Might be able to find a match on Ebay
DON