Where to source a clear glass to replace the filter on a Nikon Z9?

I'm looking to modify my Z9 but I can't find a reliable store to get the glass alone. The stores I have found offer the service to replace it but I want to do it by myself because I would have to send the camera for too long, several weeks at least. I prefer European stores if possible but really if there's a good option in Asia or America that's fine.