I think with gun disarms it might be helpful to drill them with airsoft pistols or some such in order to see how effective they are. Please use eye protection of course.
Rubber band guns are the go
They cost almost nothing are leagal almost everywhere and as an added bonus to stop getting shot you can grab the top of the gun which with a real weapon would be the slide or the hammer.
I have trained a simpler version than the Krav(I will hunt down youtube see if I can find it). And although I have never taken a gun off someone but the theory works well for bottles which I do a lot.
But in alll honesty it would be much of a muchness so long as you are good at it and are comfortable.
A few things to consider.
Find an inside of the arm and outside of the arm method. They are the two most comon places that you may find yourself. My theory being you will see gun have a **** fit and grab the thing and then have to work from there.
Train from the draw If you can deal with the hand before it reaches the gun it will make life much easier.
Also train rifles which iinvolves different mechanics in removing out of someones grip
And this is just a me thing I don't like to strike. I have enough trouble ripping things out of peoples hands without the added stress of taking one hand off to hit people with.
(Although I might throw a knee or headbutt in)
I've found one possibility so far that isn't unreasonably far and looks like they might know their stuff but I'd like some feedback if anyone is experienced with this group first.
Hisardut http://www.hisardut.com/ the head instructor is Alon Stivi and the school is located at Newport Beach anyone worked with this guy?
Find something that focuses on immobilization and striking. I hate to say it, but KM has the right idea with always throwing in a knee or an eye jab.