I've seen nice envelopes at Michael's crafts for people who want to design their own stationary. I haven't looked closely, but they may even be acid free.

Try Impact Images 2683 Hwy 45 S, Jackson TN 38301. They have a brochure for "crystal clear bags" - envelopes that can be sealed or folded shut. Many sizes; I have a couple of boxes and was very pleased with quality.

M

i've had good service at www.paperaccess.com. You'll need to buy 100 envelopes, but it is not very expensive. Just means you'll have lots of projects! Your cards will look beautiful!

Here is a link that might be useful: see-through envelopes

Impact images has a website. They carry both the clear and the reguklar envelopes...all sizes.
http://www.impactimages.com

If you want clear envelopes to put finished product in stampin up sells them they have plastic strip that removes for sealing the package they are about as big as a large card. I don't know if you have any stampin up people in your area. if you are making smaller cards try a candy making section- walmart or another store they use them to put suckers in. they don't seal but you could use clear scotch tape and I know they are cheaper than stampin up