So I searched on google for a few minutes even though I don't own a mac (Yea this question was actually bugging me that much
)
Mac uses an IME called Kotoeri apparently.
I found this table.
Anthy : xwi or wyi - ゐ
Anthy : xwe or wye - ゑ
use F7 to get katakana versions
MS IME* / Canna: wi - ゐ
MS IME / Canna: we - ゑ
Kotoeri / SKK: wyi - ゐ
Kotoeri / SKK: wye - ゑ
If that doesn't work then i don't know what will.
