I went looking for a couple of anniversary cards earlier this week (to give my folks for their 60-something'th, and my husband for our 20th). I found abundant birthday cards in every possible variation and specification. I found Congratulations, Thank You, Thinking of You, Friendship, and Carpool Lines. I finally found a very few anniversary cards, providing very little choice in style or sentiment.
I guess I shouldn't have been surprised. Fewer people married for fewer years, with years passing before any remarriage, means fewer anniversaries. I also suspect that people are less likely to send anniversary cards for friends and family who are on their second or subsequent marriage. I would guess also that divorced people, so numerous in this era, don't get much pleasure out of sending anniversary cards: "Congratulations on staying married when I couldn't!"
In the end, I bought a blank card for my husband, with a photo of a boy and girl dressed in wedding garments (she was kissing him). And I used one of my own photos, a couple in silhouette walking on a beach, for a card to my folks. I wonder how many people make do in a similar manner, and how many drop the idea of sending a card -- shrinking the market further.