used Block magazines come up on ebay quite often, you could put a watch for each issue and get them that way.
You could check with MSQ and see if they have back issues for sale, or digital issues.
You could put a Wanted ad in that section here or other online quilt groups, tons on facebook.
really depends on how badly you want to make that particular quilt. Often there is a fb group for particular sew alongs and often the patterns will be in the files.