Pete, your local "used auto parts mart" (AKA junk yard) has hundreds of them all sizes and shapes! Commonly known as a "fuel door hinge"! Got mine for 3 bucks!!
I suspect the problem where two latches are used is because the oil door / cowl will flex to some degree causing the latch arm to slide out from behind the cowl lip. I bonded the cowl portion that I cut out to the back of the Vans oil door and it is much more rigid and lighter that a metal door. Time will tell but I think it will be fine.