Lego minifig compatible Custom SI-Dan Toys G4 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 G4 has a larger Holster to fit pistols like the G19t and M23.
The following pistols have been tested and DO fit in the holster.
M1911
P226 Navy Seal
HC-1
MK44
08 Luger
M1917
Tactical Spy Pistol
M9
M1851 Navy
M23
Auto 9
Night Hawk
G17
Desert Eagle
M92FS
P99
P228
Colt45
M10(lose fit)