I just got some from Heinrich b/c I remembered OWH recommended them and Amber was so lovely to help me pick the right one b/c there are a lot of choices. I just checked the order and it was Arrow bright white 1000/30.50. #1A2ARBWT. I did order all 3 standard sizes so I could get free ship cuz that's expensive with them. The CS lady needed to ask me something and she was SO SO nice I cant even tell you and sent me some samples of other ones that I am going to hold onto. They also do kraft for people who like that.
Heinrich Envelope
I am looking for a heavy envie so you dont see the card through it and to protect embellies. These were much better than what my local stationary store was offering and a bazillion times cheaper, but I would prefer even heavier. I would love it if they were like the CS itself and I could make them but not in bulk.
FYI Amber has an ebay store with clear ones and she is just wonderful. The link is any of her posts (sprtchick)
You could look at Marco Paper. I know they supply my LSS. Especially if you want colors and finishes. I liked their booth at a show but I was surprised when they didnt know pound weights of their stuff but maybe they were just show help? They were very nice people.
https://www.marcopaper.com/
I have a Jam paper store in my area and I drop in there sometimes-they have clearance sections that I look at. You can get small packs (25) if you just want something for one mailing...I was getting clear there too. They also do blank small shopping bags if you wanted to decorate yourself for gifts, have ribbon, etc.
JAM Paper: Envelopes, Paper & Office Supplies in Every Color