Yeah, it's true that electronics stores have pretty much completely ditched DVDs, but it's not totally impossible to find them still. Comic book shops and comics stores in the city center often have a little shelf dedicated to DVDs and Blu-rays, especially movies and series that have a dedicated fanbase. Try asking the shopkeepers directly, maybe they can order what you're looking for. Then there are still stores from chains like Feltrinelli and similar that keep some stock, though less than before, depends on the city though.
Honestly the secondhand market is pretty much the richest one now: Subito is an option, but also consider eBay which sometimes has reliable sellers with good selections, and vintage shops around the city center work too if you know them. Another option is searching on the internet specifically for "DVD shop" in your area, you'll see what comes up - every so often in the outskirts there are still some old-school stores that sell DVDs, especially ones that do rentals too.
The thing is people are selling off the DVDs they have at home now, so finding them in good condition is possible at decent prices too. If you're in a medium-large city you should manage just fine, just gotta be patient. For more recent or rare titles you might have to wait for the right opportunity, but classic films from the 2000s that you mentioned usually pop up pretty often in the secondhand market.