3 inch Leitz 2-ring Filing Binders. (Some 2inch ones available)
Used condition
Office business binder

MANY available.

$5 each or
$2 each when buying 10 or more.

Most black marble coloured.

Could work great as sports card Binders (would just need to make new holes in the card sleeves)

Fits A4 size paper
Space inbetween rings: 8cm
Height: 12.5 inches
Width: 11.25 inches