I had the same problem with the valve on my oven. It's true that the part cannot be found. I finally rolled the dice on a used one and got burned (pun intended).
Why are you adverse to a new 3-burner unit? Do you use all 4 burners? I eventually replaced mine with a "scratch-n-dent" (ebay - half the price of a brand new one) Atwood/Wedgewood unit and I love it. The front burner is a "power burner" and gets water boiling fast. Fries stuff up quick too. Much better than the 4 smaller burners IMO. Funny thing is I haven't used the oven yet :-\