I would totally try to gain enough bp from battle royale to get these items buuut yeah it's very slow and almost depressing how little bp you gain from the royale.
I might try and keep battling in the royale but it is a joke and my mons aren't like battle ready sooo.
If you're not sure what I mean by power items, I mean the EV training items.
I'll trade spare Kartana and apricorn/beast ball Pokemon for them
Power Lens, Power Anklet and Bracer acquired, many thanks to JustJames for those
Destiny Knot acquired, many thanks to Robotree!!