I think you're right Doggie although Lotus may be stocking the (Sparco made) clips. . Lotus doesn't seem to keep upholstery related parts though, so if you actually require, for example a replacement seat cover, getting one can be very difficult if not impossible.
I may be the first person here (USA) to have experienced a warranty repair for this problem prior to availability of the clips. Consequently my driver's seat was repaired twice. The first time since the clips had not yet been introduced, it was left to the servicing dealership to figure out a solution. In process of that, the original seat cover was damaged by a clumsy (since gone) tech. Lotus could not or would not supply a replacement cover even when an offer to pay for it was extended. Appealing to Sparco had the same result: no joy. Fortunately, a local upholstery artisan was able to repair it seamlessly so there is no visible evidence of damage and the seats have remained tight.
The situation may have changed since then . Perhaps they will or can now sell you what you ask for but whatever you do, don't let anybody try to fix the seats without the proper parts. That would be a waste of time and potential total fail. Unless proven otherwise, don't ruin one of your seat covers in any other way either 'cause you may be ordering up a whole lot of custom upholstery and your guy is going to go nuts trying to match the leather!
However, the clips are a 100% repair.
'17 Evora 400 MT