Taxtools.com (CFS Tax Tools) has envelopes that work with Lacerte (and other programs).
It's a great company, and the prices are some of the best around (a lot less than ordering from Intuit..)
Check out their software offers too. Very useful (as @George4Tacks) says "the swiss army knife" for tax professionals.
If a post answers your question, click on *Accept as solution* for future searches
Like many of the links here, my like to this one is broken. I do have https://www.amazon.com/Double-Window-Return-Mailing-Envelope/dp/B003CRI56Y
and https://www.goldenwaybf.com/printed-products/lacerte-tax.php who are very pleasant to work with.