There are a couple of "specialist" lenses still around in T2 mount, whether they're the same lenses under different brand-names or actually from different manufacturers I don't know.
I'm thinking specifically
Samyang mirror telephoto lenses ... I've got an 800mm f/8 (which has it's own problems), and I seem to remember seeing a couple of ultra-wide fisheyes recently, but took little notice 'cos the Peleng 8mm I've got serves my purposes when I feel the need
Be aware, Meyer Optik are (and have been) in a "state of flux". Whilst they do still offer some of their range of six lenses in M42 mount at seemingly attractive "discount" prices, I do wonder if a "modern" 30mm Lydith at 599 euros
https://www.meyer-optik-goerlitz.com/en/lenses/lydith-30-f3.5 is that much better than a second-hand "original" from your favourite on-line auction site for about a tenth of the price!