Some people enoucnter a bug where their playable character is not recognised as elf trained(the bug is not linked to your gender since i have been able to use elven armors on my female elf char they were also equipable on Solas).
About Sera not being able to use elven armors, while some people claim this is a bug i think its actualy working as intended since she was raised as human by humas and never cared to learn anything about elven colture since she detests it(thus counting as human trained which is what she can actually equip).
Dalish armor shematics i encountered in my game were:
-keper robe ones(light armor, shematic is a fixed drop from the last dragon in Emprese du lion)
-dalish medium armor one, shematic can be bought from Hissing wastes dog merchant
-according to some other people more of them exists, not sure though if as random drops or part of extended inventoires of merchants(by perk), bear in mind though that if its by merchant perk you might have to visit the merchants many times since they get 1 extra shematic but they change with time(not sure if simple reentering the zone is enough for the merhcnat to reset and recive new random shematic or you actualy need to finish a quest or something else for it to reset-havent tested it myself so only going from what other people say on forums).
Also another important thing to mention both dalish shematics i got had no upgrade slots which made them consideraby weaker to other avilable armors, so if anyone knows of any dalish shematics avilable with upgrade slots do plz let me know.