so, this is hard nut to crack.
JG has none and i assume Daisy.
you could try here.
https://www.tmacsairgunservice.com/ he had some last year i bought some from him.
now that leave the owner to try to make a replacement.
the problem for the Diasy 7-7 seller and buyer is there are many pistols in very nice condition but they have a broken rear sight.
now i made 2 replacements and i thought if was easy enough and anyone could do it i would share but it was tedious at bast to do with just a hacksaw and files.
i used a piece of 1/2 x 5/8 aluminum bar stock and a Ruger pistil rear sight off Ebay.
the sight is plenty nice enough and the bar stock fit the sight channel but it was the ability to keep it square and cut the notch for the sight to sit in.
the sight and the block are just epoxied together and the block will slide up and down and with that and the sight adjustment you would have no trouble make it work and it will give you a long sight radius
i made them for myself but it someone could make a 3D printed base for the sight then anyone could merry the two components together with epoxy