Asked for this in 2 threads already, heres one of them:
http://www.thebuddyforum.com/demonbuddy-forum/demonbuddy-support/54846-uielements-iteration.html
As you can see, noone seems to know the answer :/ (apart from devs ofc, but they are quite busy i guess

)
Its probably either part of one of those object managers or its somewhere in this SNO, which i have no idea what is stands for.
ZetaDia.SNO.LookupSNOName(SNOGroup.UI, id ??);
This looks kinda interesting, it doesnt return UIElement, but its still something, but i have no idea where to get the id, i even tried to iterate ids from 0 to 10000, didnt really find anything.
Theres also this:
Zeta.Internals.UIElement.FromHash(ulong)
This might also lead somewhere.
Then theres ACDList and RActorList, but UIElement is not an Actor, its parent class is NativeObject.
So im kinda clueless :/.