The most common "plastic" mags would be either the Thermold (both Canadian and American versions) and Orilites (Israeli made). There are numerous posts about the Thermolds and Orilites. For the most part, most of us here would tell you to skip them and stick with USGI mags.
The LEO/Gov't use only mags are post ban high capacity mags. This means they are magazines that hols more than the allowed 10 rounds of the 1994 Bill. They are to be had by and used by ONLY Law enforcement officers and Military personnel. Having these mags is against federal law and can land you heavy fines and/or jail time.
Yes, the BATF may have larger things on their minds at the moment, but just like not having a seat belt on when getting a traffic ticket, may be added charges that may end up digging a bigger hole than you ever imagined. For instance, say you did get a traffic ticket and had a magazine floating around your car, or you just stopped off real quick to grab a drink on your way to the range, and you have a magazine in plain view in the back of your SUV. A somewhat ordinary ticket now leads to Federal charges. Yes, while it may be a stretch, it is possible. The Son Of Sam was suposedly caught by a parking ticket, after all.