Turns out Google Books does support searching by ISSN, using ordinary fielded search syntax, although I don’t believe it’s documented anywhere.
Mostly what you’ll find is digitized bound journals from libraries (that is, digitization of some volumes of the journal, probably not all of them, which may or may not have full text access). Sometimes things that physically look like monographs but are published serially also get ISSNs, you might get some of those too, not sure. Has to be in GBS, and GBS has to have ISSN metadata for the record, not sure how often that happens.
with or without hyphen, both seem to work.
But don’t try to put phrase quotes around the value, that (oddly?) doesn’t work, with or without hyphen.