There are lots of constellations around which should have the 10-sided crown but have the round crown. Are these 10-sided crowns still available from Omega or elsewhere, or is it the common practice to replace them with the round more usable crown?
I don't believe the ten sided crowns are available from Omega anymore. Either find one as a stand alone part or from a donor movement, or find a watchmaker who somehow has a stash.
Not available any longer. Occasionally some pop up on eBay but there are also fake versions so be careful. It was/is common to replace crowns at a service, particularly these ones as they weren’t the easiest to grip and turn.