What exactly are you looking for? Specifically, are you looking for one that mounts to the tang holes or side mount? Any idea on the model or brand, vintage you're after?
I'm not 100% to be totally sure. I'm actually trying to help out an elder friend of mine that thinks computers are the devil.
I did gather from our conversation this evening (he's in Alaska and I'm in Idaho) that he wanted one that mounts to the tang holes and NOT from the side.
The only two manufacturers he was aware of are/were Lyman and Marvel, and didn't seem to have a preference. He loves the rifle in question, but his eyesight isn't what it used to be and he needs a differnt sight to be able to shoot the old girl.
I don't know if he knows that, but I'll run it past him and see if he's interested. Usually he views Aluminum gun parts in the same way he does Communist activities, but who knows...maybe he's softened in his latter years.
If it's a later 1930's to 1950's 99, then a Redfield or Lyman peep is more "correct" for the era. Some of these you have to be careful of, they push against the wood on the side. Here's a Lyman 56S.