95% sure he uses Luca shirts for majority of wear.That may have been true a long time ago, but is definitely not still the case.
https://www.permanentstyle.com/2015/03/davino-shirts-the-zenith-of-visiting-italians.html
lists 3 traveling Italian shirtmakers at different price points.
I personally have had some shirts made by him recently, it took 5/6 fittings in person in london (although I have specific bodyshape)