Don't know if this would be the same at Walmarts everywhere, but when I was in Walmart yesterday I noticed the lady stocking the cards wearing an American Greetings apron. I went up to her and asked her what she does with all the extra envelopes when they are re-stocking, and explained I'd love to have them if she was going to throw them away. She told me to meet her the day after Mother's Day (or the day after any holiday) and she'd give them all to me. YAY! I'm going to go down there and meet her for sure. I'd asked Walmart a long time ago about this, but they said they outsource their card stocking to American Greetings, so couldn't give me the envelopes. Glad I happened to run into the lady.
It's worth asking about....can't beat free envelopes in every color.