e.lectronic
I can't help but notice that this is your first post, so let me give you my opion on what your asking for.
First the M&P is a safe action pistol, that in all reality does not require a safety, if no safety makes you feel uncomfortable I can understand that, with practice of carrying a firearm, the comfort zone does get better. If you will notice all the Glocks have never had any kind of a safety,and that is becasue it is also a safe action pistol. The magazine safety is something that in a heated battle could be very problematic. If you have to do a tactical reload and you still have a round in the chamber when you drop the mag, the time to reload, the gun is totally useless. I tend to think of things in real time situations and it is one less thing to think about, when the $--t hits the proverbial fan. If you ever have the opportunity to read some of te things that Jeff Cooper wrote you would learn alot about shooting philosophies, one notable quote is with regard to safe action pistols and goes like this "adding a safety to a safe action pistol is like looking for a solution to a non existent problem" ! If you are still determined to have a safety, by all means do it, and I would suspect that if you can fiind one with thunb safety adding the mag disconnect would be a very easy task, and I would even bet there are guys on this site that would send you the part because plenty of guys remove them, myself included! Don't know if this helps but good luck with your search.