I am making a pointy-ear army myself for Space Marine so may be able to help here!
Best STLs I have found are Lord Chronos, however after some searching it looks like they are no longer hosted on Cults3D. Try searches for Lord_Chronos, there may be some buried on some file sites somewhere.
Mighty-minis-
UK does have prints themselves for sale - however Albertorius has advised that they are not licensed, so not sure how long they will be there for, although hopefully now he has obtained this
https://www.mighty-minis-uk.com/Epic_40k_Eldar/cat8022654_998143.aspx
Again not STLs, but Vanguard Miniatures do an awesome range of almost-Eldar. I've got some Guardians, Fire Dragons, Exarchs from them in their Defeat in Detail Eloi range
https://vanguardminiatures.co.uk/index.php/product-category/defeat-in-detail-6mm/
Finally Miniwars is a great resource for lists of official minis and also proxies that can be used for various things - found this super useful for when you can get a proxy, or need to get the wallet out for the old originals from eBay (like the Avatar - which
AFAIK has no proxy, but is a free unit in Epic
SM and so you need to get really!)
https://miniwars.co.uk/epic-40k/miniatures/
Hope that helps, or at least gets him started.