Lego minifig compatible Custom SI-Dan Toys G1 Tactical Belt, fits between the minifig torso and legs and it has a clip at the back which allows you to attach grenades or knives.The following pistols have been tested and DO fit in the holster

BrickArms M1911
BrickArms P08 Luger
BrickArms M1917
BrickArms Tactical Spy Pistol
SI-Dan Night Hawk
SI-Dan G17
SI-Dan Desert Eagle

The differences between the G1 and G8 is the clip is on the other side and the G1 has 1 larger pouch instead of 2 smaller ones.