Most screw-ins of that era have the same thread size so really all you have to do is pick the one that you like.
I grabbed a few of my loose adjustable aperture sights to show you. (No, they are not for sale.)
Top is a BSA, it's the same tread pitch as the two P-Hs under it.
Notice that they are taper threads, they get tighter the farther you screw them in.
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Like I said it's really up to the taste of the shooter.....Hope this helps.
BTW....eBay is always you best bet (there are several on there now) but they are not cheap......Expect to pay $60-$80 in good shape.