I picked up a pair of el Cheapo GSG Firefly .22 Pistols on sale from Rural King. One for me and one for the misses...

They come with a threaded barrel, but unfortunately, they are threaded as M9x0.75 so I need an adapter for them, so we can put Cans on them.  Ideally Amazon would be the best place, but I found every size, but 9x.75 to 1/2x28....

I googled and found a few other places, but never heard of them any of them... Thought I'd check here.

Also, with my old ass eyes, I seem to take to green night sights better than any other color.
Does anyone make Night Sights for the Firefly? Probably Not.

Well, I guess I'm going to try a pair of these from LethalEye.com   and see how they do...  
I mean its a cheap ass .22, not like a Nice H&K or some other spendy gun...

I just searched for gsg firefly 22lr thread adapter and found a bunch heres one site

https://hughesprecision.com/product/hughes-precision-sig-mosquito-thread-adapter-12-28-wfluted-thread-protector/

I was going to suggest HUGHES PRECISION.  I'm glad the last poster steered you that way.  I have purchased several thread adapters from HUGHES PRECISION and they have always been a perfect fit.

I've never ordered from Hughes, but it was the best looking adapter I saw through limited research.