This is the closest I can legally get to an M249 SAW. It's a civilian transferable lower with the MCR belt fed upper and the same trijicon scope that the SAW uses. :
M249 - Official PLAYERUNKNOWN'S BATTLEGROUNDS Wiki
S&T M249 PARA スポーツライン レビュー | 船長の銃改造記 - 楽天ブログ
M249 Squad Automatic Weapon | Military.com
M249 light machine gun - Wikipedia
A&K M249 MK46 SAW LIGHT MACHINE GUN WITH POLYMER RECEIVER AND BIPOD - BLACK - MiR Tactical