If it was me.
Once a tyre starts getting harder to find or harder to obtain can be a good sign to start looking for other options. Eg Another brand, size, or even a different rim size.
Harder to get, higher the prices go, and over time will only go higher and if you find yourself in a jam once again it becomes another headache..
These were the cheap version of simex centipedes right? They were a really limited use tyre even 15 years ago. What kind of driving and car are you fitting them to? Do you actually need a tyre that's completely useless on road?