caster for MIM Roma Ico Parisi desk chair  

Vintage casters are a challenge. They often wear out and fail, eventually. Like upholstery, though, it's generally considered acceptable to replace with appropriate new(er), similar or better quality products. You can always keep the originals (and keep up the search for OEM spares) while still enjoying use of your chair. It would be ideal to maintain our treasures as a museum might, but the reality is that many of us would rather live with and use them.

Thanks. The thing is I cannot find any newer version that can fit in it 🙁

Hmmm... Can you pull a remaining caster, measure the mounting stem, and post a photo of it?

Here in the US, Shepherd seems to supply most similar-style ball casters to the furniture industry, but their mountings are only available in English standard. I would assume there is a European counterpart supplier.