There are multiple options, including all of those mentioned above.
Personally, if money is no option, check with MidwestPX as they offer limited capacity PMAGs (both cut-down mags and blocked mags). They are 100% functional with a huge range of ammo I have used in them and will serve you well!!
Here is a link to the magazine section of their website (and Ty...the proprietor...is a great guy to deal with and a sponsor of the Hide):