Cleaveland tools has one that is pretty nice. I have used it in my old 7 and now on the 14. It has a spring that will pop open once unlocked. You will know it before flight if it is not locked.
Thanks forthe replies. I googled a variety of combinations of "oil door" and "spring" but it's not what I was looking for. I saw an oil door that was spring loaded where you pushed down to open and the oil door would spring back closed. It was a compete assembly. Sold by a company called Justrvparts. I can't find any information on the company
Here is the one I used. It both eliminates the hinge eyelets from view on the outside of the cowl, and gives a spring to open it. I then used an aluminum door and some bent angle to stiffen it. The door is held in place with a single hartwell latch.
What Bavafa and Andy have linked to is what you are asking for. The waybackmachine has the web site but no pictures. The description is the hidden hinge that Cleaveland tools now carries.
Sounds like he's looking for a door that opens inward, not out, and the spring shuts the door. I've seen them, but would say that you need to be sure the door will clear the fill tube and any other structure before committing to a design like that.