I think most people here just cut the cam off of the stock reflector. For a deeper one you could use the reflector from a new rebel mag. If you just realy want to buy a new one this may be an option, it will fit your maglite but you have to bore the opening to 16mm for the P7. This may be another option if you dont have the tools needed to bore out the other one, its 5$ more but it has a 15mm opening so you could enlarge the opening just a bit using a razor knife ( i have done this in the past). Just be sure to open it large enough to the reflector does not touch the wires to the emitter by accident.
I had the same question and ended up sputtering the stock reflector. The beam has a perfect hot spot and is probably the best your going to get before having to increase the head size. http://www.candlepowerforums.com/vb/showthread.php?t=249875
KD P7 Reflector (52.66*29mm) SKU: S004994
This reflector works far better than any other Chinese offering. It needs some material taken of the top threaded part for the mag bezel to screw right down.
The KD reflector gives a very nice finished appearance, one of my mags below.
You could always use a Fivemega deep reflector. I don't know whether any modification is necessary, you could always ask Fivemega.
Norm
i have 4c mag with malkoff p7, i use stock mag reflector that i op'ed, and cut off the cam, works great. good hotspot, and plenty of spill.
i also have 3d p7 mag with FM deep reflector, it has tighter beam and less spill than stock reflector of 4c, it throws farther.