to the best of my knowledge, there is no modern edition of anything
written/forged/edited by iolo; i think almost all of the ms. are at the
national library of wales in aberystwyth. a good place to start looking would
be the Report on Manuscripts in the Welsh Language by j. gwynogvryn evans, 2
vols., 1898-1910 (london: historical manuscripts commission), and another
thing to do would be to contact the library itself.
there are so many unedited medieval irish--and welsh--manuscripts that it's
laughable. i once was talking with a professor who specializes in jane
austen who was literally green with envy and drooling when i told him about
the unedited mss. i was going to be dealing with for my dissertation. i
mean, the standard edition of Kulhwch and Olwen only came out in 1988! you'd
almost be better off compiling a list of what little *has* been done, and
going on from there.