Alright, lets see if I can kick some life into the forum.

So, I was wondering if there is any information on regarding the use of chlén-hide outside the area of the Five Empires? Can cultures outside of these areas be expected to fashion items from the same treat chlén-hide or is it a "local" thing?

The reason is that I'm sketching for an idea about a empire located on Tékumel but outside of the area of the Five Empires, and thus it would be good to know if they should reasonably be using chlén-hide or not.

It would seem reasonable to allow some form of Chen hide use- after all on earth leather working an taaning seem to be universal outside the most prImative areas.
But without the tanning guilds perhaps techniques are not as advanced (or for a counter view more advanced without the restrictive effect of the guilds and theocracy ?)
What are you thinking of armour or blades mainly?

In terms of "official" publications, I don't think there's anything definitive on whether the technology of Chlen-raising and Chlen-hide processing is known outside the Five Empires. It's a pretty resource-intensive process, so might not be done by nomads or cultures with little social organization. You could plausibly have it any way you want. Maybe your empire is mineral-rich and uses bronze?

Is there anything in the books on different subspecies of chlén? After all, different sub-species of chlén may have different qualities of hide, and be found in different regions of the world, so perhaps this nation may have chlén-hide products which are easier to produce but of lower quality, or vice-versa.

There is nothing on sub-species that I know of. There are wild populations, but they are also thoroughly domesticated. There are clans dedicated to raising and breeding them, and the Temple of Avanthe even has a "faction", the Joyous Burden Society, dedicated to advancing the state of the art of Chlen-breeding.