AustriAlpin quick release cobra buckles are probably the toughest, best-looking, rugged buckle you could use. Available in various sizes (50mm being the most popular), they are available in black, matte black or coyote/tan, with other colours due shortly.
We stock the big button type, which are easy to undo when wearing gloves and the quick pull sliders work really well on rigger type belts.
We stock our own quick-release belt with 1.5m of nylon belt which blends really well with either the black buckles or the coyote.
25mm are also available, although stocks are low currently and we are waiting for more to arrive at the time of writing.