My guess is that they are all super rare things you can steal.
There is a contraband list where zones are, if known, listed, here:
https://elderscrolls.fandom.com/wiki/Treasure_Items/D
Unfortunately, nothing for the items OP is searching for. Also checked UESP, nothing there either. Was worth a try, though.
All I can add is that stolen items are logically related to the zone they're found in (completely random if found in the bags that you get from Mirri's special ability, though, and sometimes festival reward boxes). For example, Hermaeus Mora related items could maybe be found in Craglorn where the Seekers Archive is. I don't know for sure though.
And it's definitively neither in Deshaan not on Vvardenfell either. I go thieving there so often and never came across these things.
DarthCuddlefluff wrote: »Although that still doesn't tell me exactly WHERE or WHO to steal from.
aleksandr_ESO wrote: »http://esolog.uesp.net/viewNpcLoot.php?item=Shard+of+the+Ideal+Masters
http://esolog.uesp.net/viewNpcLoot.php?item=Shatter-Shard+of+Mehrunes'+Razor
https://esoitem.uesp.net/viewNpcLoot.php?item=Illegible+Page+From+the+Oghma+Infinium
https://esoitem.uesp.net/viewNpcLoot.php?item=Dwemer+Tonal+Diagram
https://esoitem.uesp.net/viewNpcLoot.php?item=Dwemer+Animunculi+Schematics