Folio Society has some books with wide margins, but they're pricey and the selection is somewhat slim. After this Library of America editions have some of the widest margins in the business, but at 5/8 - 6/8" they're still not great. (Their selection is nice for American writers with scholarly editions, but thin beyond this.) After these, Norton Critical Editions and Penguin Classics are some of the better ones at inexpensive mass market with bigger catalogs, but generally they're still abysmal.

The only prudent option seems to be to buy/obtain a text and then self-publish your own interleaved edition or print/reflow to provide your own custom margins.