Reddit mentions of 50mm Circular Welding Lens, Green IR Shade 4

Alright, well, after more than ten hours of searching, I came to the conclusion that what I'm looking for doesn't exist. In case someone finds this post while on the same search I'm on, here are my findings:

The goggles I ended up using were the Hot Max 25031 50mm lens welding goggles - these were one of the few goggles I couldn't find that weren't the US Forge brand goggles, a pair of which I also purchased. The latter are very uncomfortable, but the strap is fantastic. The Hot Max goggles were notably more comfortable and durable, but the strap is uncomfortably rigid and pops out of the goggles. So, I swapped the straps.

Now, unsurprisingly, neither are really made for comfort or long-term use. I ended up using quick-set superglue and a sheet of thin black foam from hobby lobby to add a small amount of padding around the bridge, and now they're very comfortable.

Welding goggles come with a shade 5 lens by default, which is far too dark for clear vision in normal daylight. Remembering this from my childhood (my dad was an engineer), I purchased 50mm shade 4 lenses in the same order. They are typically sold individually, and not as a pair. Be sure to keep that in mind when ordering.

Welding goggles seemingly universally have interchangeable lenses. Both the US Forge and the Hot Max goggles accomplish this the same way - the eye caps unscrew. Both goggles came with a glass lens (which is UV 400) and a polymer tinted lens. The Hot Max goggles came with a rubber washer to prevent the lenses from touching, which the other lacked.

So, basically, buy a pair of both (less than 20 bucks) so you can swap out parts and have backups, get a sheet of thin foam from a craft store and make them comfortable via superglue, and buy some shade 4 lenses. You're looking at roughly 30 bucks total for entirely functional and comfortable goggles.