I just searched the ISSN portal, and "think: a journal of poetry" retrieved nothing:
https://portal.issn.org/advancedsear...rch_id=3821314
WorldCat, managed by
OCLC, is the world's largest network of library content and services. WorldCat contains a record for this periodical, but (unsurprisingly) no ISSN:
https://www.worldcat.org/title/think...oclc/913243813
Depending on your deadline, you might encourage Brian Palmer to request an ISSN. The process seems pretty painless, and US publications don't have to pay the registration fee that other countries' publications generally do, because the Library of Congress covers the costs.
http://www.loc.gov/issn/
Brian Palmer may wonder what's in it for him, though, if the journal has been getting along quite well without one.