For some oversized records - military certificates, for example - I use an oversized 3-ring binder. It is a box style binder and has ribbon ties to close.
The particular one I use is standard scrapbook size - 12x12 inches. It is a 3-ring binder and comes with acid-free sheet protectors.
Since we are not supposed to discuss prices or commercial matters on these boards, please send me a PM if you want the brand and style number.