I know there's a guy in Seafolk Vollave who gives you one of each but I sold mine ages ago thinking I don’t have any use for them and now I have a shiny Electabuzz who needs it.
Electirizer:
Battle Tree (32 BP) Held by wild Elekid and wild Electabuzz (5% chance each)
Magmarizer:
Battle Tree (32 BP) Held by wild Magby and wild Magmar (5% chance each)
Source Source Both of these are the repeatable methods to get the items; I'd suggest buying them from the Battle Tree unless you want to item farm from wild Pokemon.
Hope this helps.