COLLINS SESTET

The Collins sestet contains three stanzas of 6 lines each, for a total length of 18 lines. Couplet  rhyme is used, 3 couplets to each stanza, but each of the three stanzas ends with a repeat of the final couplet from stanza one.  The meter appears to be iambic tetrameter.

The only example I've found is too imperfect to include here. I'm looking for better examples.  Hang in, please.