Mother's Day is celebrated on different dates in different parts of the world - in the US, Australia and Canada it is on Sunday, May 13
For other countries you can check here http://www.mothersdaycentral.com/when/
Barbara Reese has very kindly created some designs especially for the Cavalier Matters charity [supporting Cavalier health research and rescue]. These are ONLY available from the http://cavalier-gift-shop.org/greeting-cards/mothers-day/cat_41.html
Your choice of Blenheim, Tricolour, Ruby or Black and Tan.
You could leave the appropriate page up as a hint to your OH that you would appreciate a card from your Cavalier - or if they are as clever as Dougall, they can order one themselves!