Re interlibrary loans, just an added note that most large libraries, and
especially library system headquarters (for one of which I work), also have
OCLC. But you can't do subject searches in journals on OCLC; all they can
do is find what libraries have the issues of the journals you want.
However, libraries can do database searches for you on the specific subject,
encompassing all languages included in the database. Ask your reference
librarian, public or private.
Note that this service is free to the public, at least everywhere I know of
(in New York State). Actually getting the articles may cost, depending on
the loaning library, and especially between countries.
Re the Hag of Berre, I can't help much on the academic or Irish-language side,
but I studied the poem with Catherine McKenna of Queens College as an
undergrad (she is on this list, but probably too busy to respond--at least
I haven't seen her name pop up yet. Hiya, Catherine!). I suggested it may
be the lament of an old goddess, though of course the poem is not that old.
Facinating study--I'd love to see your paper when it's done!