Q: Where do you find a birthday present for a cat?
A: In a cat-alogue!

Explanation: A catalogue is magazine that shows things that someone can buy; you might see a clothing catalogue, an electronics catalogue, …  You can see images from a 1945 Sears catalogue here.  And from a 1980’s Sears catalogue here.

Of course “catalogue” begins with “cat” and that is what makes this joke funny.

¡Happy Birthday to E. A. S.!