Can you send a Jehovah witness a card for the memorial of Jesus?

Absolutely, but I do not recommend sending a store bought one. Those one's might have simple things that the witnesses do not believe on. It could have a picture of Jesus on a cross, however in The Bible it states that Jesus was tortured on a stake, which is just a long wood pole.

I'm sure a witness would appreciate a card that was home-made by you.