Every package that I know I am shipping to a fellow shop owner gets a envelope of cards that says
"Support these Etsy Shops. Please take as many cards as you'd lilke. Add your own Etsy shop cards, and then pass this along with your next shipment. Spread the love and help promote."
I trade often, and am always looking for more cards to put into my shipments. I put 4-5 different shop cards in each package. If interested, convo me, and I'll get you my address to mail as many as you'd like to.
Would absolutely be interested in trading cards (mine have a coupon code on them) or sending mine out to others that are doing something similar. Would love to be part of your system, Bayleaf.