Forks with such long steerers have always been rarer as the people who ride bikes this large are equally uncommon.

We build forks in advance for our own production and also supply them as replacements since 1 inch threaded forks are not as common... it does get a little spendy once you factor in the build and the finishing and use longer steerers so we can cut and thread them to fit. We also tend to build bicycles for a lot of uncommon people.

I have a fork with a 260mm steerer here but it is worth more than the bike you have.