I'm currently working for a local Marine Fabrication / Re-gear / Re-power business. We just made something very similar (although industrial grade to handle the intended use / abuse) for a Raised Pilot House on a Tug. For the stowed latch we located a ball and socket fitting (typically used to hold watertight doors open when desired). The socket is rubber and the ball is plastic. They work really slick and are pretty economical at our wholesale corporate cost at least. I'll try and get our source or PM me and I'm sure we can work something out.
For yours; a smaller version would be more than adequate, if available?
For ours; I fabb'ed a hinged / pinless over center link that tucks in-between the seat portion and the leg portion to ensure the leg stays at 90 degrees when deployed. Also fabb'ed a spring loaded pin latch to secure the leg to the seat portion when stowed. Anti-rattle bumpers at all the tight clearance potential rattle points.
It was way too expensive to make any money off of; unless the customer is willing to cover time and materials. Ours had both seat and back rest cushions custom upholstered and other niceties though. We made our own hinges with 1" Delrin rod and 1" sch. 40 aluminum pipe, as the stainless steel piano hinge would not have survived the abusive environment for very long. The tug was originally built / used in the relatively calm New York Harbor, now it is running barges of fuel in the Open Alaskan Ocean to other ports of call. They say the Raised pilot house (done so they can see over the Barge, as it is a pinned, push style setup) moves a lot when out in open water ( as the raised pilot house is about 75-80 feet above the waterline, think of the tower style sport fishing boats but on a much bigger scale).
