I have some experience of this, as I bought a D+D with a German date wheel online, as I liked the rare-ish colour dial. The day wheel is a generic enough ETA part, but you have to be careful what diameter it is, so that the text is centred in the day cut-out. I think the measurement was 28.4mm.
In the end I asked Brendan (webwatchmaker) to source one as part of a service. The part itself is cheap, the cost to fit depends on your watchmaker.
I have not seen a Greek day disc before, but I am sure there are custom items out there. I think the Arabic ones are aftermarket.