I think it may be hard to identify a Hurricane Squadron because of what the RAF was actually doing at this time. They were forming what they called "composite" squadrons to operate in France for very brief periods of time. They did this by taking a flights from two or more squadrons based in England and having them operate from French bases almost part time. If you go through the website:
http://www.rafcommands.com/Fighter/indexF.html
looking at fighter squadrons you will often find the phrase "Flight to France", in the May, June time frame. This means that that squadron contributed a flight to one of these "composite" squadrons.
I went through and found that phrase listed for several squadrons. 111, 601, 229, 213, 79, 242, 245, etc. It is very hard to find where these squadrons operated from while in France. They were there a very short time and may have moved around. It is also possible that Dreux was used for a short time by one of the RAF squadrons pulling out of France as they fell back from a more forward airbase.
A very brief explanation of the 111 squadron involvement in a composite squadron can be found here.
http://www.historyofwar.org/air/units/RAF/111_wwII.html
They mention that 3 such composite squadrons were formed, I am not sure that number is correct. It is even possible that the components in the composite squadrons rotated between contributing squadrons. It was a very confusing time and records are hard to find, (certainly on-line).
Regarding the Magister, this has been discussed on the (free to join):
http://www.luftwaffe-experten.org/
Basically what they say there is that there is some confusion between the Magister and the Master Mk1. There are pictures of a Master misidentified as a Magister. (The Magister is an open cockpit plane and the Master is not). The serial numbers you can find on web searches are often for the Master, several of which were left in France. They do have pictures of both kinds of planes left "somewhere in France".
While this is not a definite answer to your questions, it may give you some ideas on where and what to
search for.
Good Luck