D.520 didn't make it in time or in numbers. With the organization structure of the French Air Force the time, they were also scatered.
It was a very small percentage of the air force in total. The more likely candidates, making up much larger numbers of actual front line units and seeing more actual combat, were the earlier models. Ms.406s and Curtiss Hawks were in great numbers.
There were 67 squadrons of fighters in May 1940 according to the following very interesting link:
http://www.airpower.maxwell.af.mil/airchronicles/aureview/1985/sep-oct/kirkland.htmlHowever questionable the kill listings are there, it seems they have done some checking and probably at least have the basic numbers and breakdown of the French forces reasonably correct.
It says:
"The first two squadrons equipped with the fast and agile Dewoitine 520 entered the battle on 13 May; eight others completed conversion training and became operational before the armistice."
Another resources says 36 (maybe 2 squads of 16?) were in service at the start of the war. This same time showed the French and Belgian air forces having 780 total fighters. Of which 36 were D.520s.
While they ramped up production and rushed training as much as they could, the link I posted up there shows a very curious view on the French at the time. They were stockpiling fighters anywhere they could, but had no pilots to fly them! Trying to hide their weakness due to internal politics, they kept accepting more and more shipments of planes from French companies as well as Allied imports, they couldn't even utilize them all! While they had a large air force, only 1/4 to 1/5 of this could ever be flown at one time. They had aging pilots and had to sacrifice some of those from front-line units to help train yet more.
So, in short, even though they increased numbers that actually served during the very short Battle of France, the D.520 was a minority player. It was a star and gets lots of credit, but it didn't get the majority of kills nor did it get the lion's share of the combat.
My $0.02 is the D.520 doesn't have much place in this game. Unless we really start expanding other early war planesets more important than the French lineup, I also would say the other French craft take a back burner to other nation's planesets right now.