Re:
I've just had a chat with my friend at USE and he came back with the following:
"I've just had a look in one of our old user-guides and the air cartridge is indeed EKO Sports Total Air Cartridge. If I try and go to the EKO website listed it now takes me to MRP,
https://mrpbike.com/ they have support section that may be able to help".
My mate also mentioned, that they're a small company, and haven't perhaps always got the most amount of time to deal with "retro" on the phone. However, if you ping them a mail to info "at" use.group for retro enquires, someone will get back with a thorough answer when they have a sec.
However, the absolute goldmine of info was the original users manual that he sent me. I'd upload it to the catalogue and archive section now, but I can't see how I post in that section, or if I need to contact a moderator.
If you pm me with an email address, I can email it over too. Probably the quickest way of getting you the info!