Best places to print product detail cards?

I took a look at Staples' online website and I'm not sure what the exact name I am looking for, but the closest things they offer are postcards and invitations.

I'm looking to print 4" x 6" product detail cards to include in each package, which will have a nice image, a few tips, and probably a coupon code on the bottom. The paper should be pretty thick & premium, but I have no idea the name of the stationery I am looking for.

Any one have ideas on what these are called and where I can get them printed?

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