First, subscribe to free catalogs whose design and products you're fond of. Anthropologie and Free People are favorite catalogs of mine. Amass magazines of interest whenever possible. I've occasionally purchased lots of old magazines on Ebay, though this can get expensive with shipping. My local bargain bookstore also carries a rotating stock of outdated fashion magazines for a dollar each. When you do get your hands on a magazine, don't just recycle it when you've finished reading, re-purpose those glossy ads and photoshoots into envelopes like so:
First, select an intriguing page for transformation. This page is from an issue of the magazine Darling: the Art of Being a Woman, with which my sister gifted me a subscription.
Flip the page over, and fold the long sides in about one inch on each side.
Play with the fold to determine which portion of the image will make the best front piece.
When you've chosen a front piece, tape the sides together. I'll place an address label just under his pocket square. The action of the card flipping towards the viewer will first greet the recipient. And then his arresting stare will greet her as she goes to open the envelope.
Here are some other things you might try:
This page could be colored in, or left for the recipient to color in.
This lovely Hermès ad depicts a lighted igloo of scarves, and is suited to the season.
Let a letter be more than it's words. Let it be an event! And let the curtain go up with a flourish, not at the envelope's unsealing, but at the opening of the mailbox's door! Happy finding, folding, and sending!