The Royal School of Needlework often designs samplers/embroideries/needlework pieces as patterns and/or kits to commemmorate royal occasions.
Here is a design created for Elizabeth II's silver jubilee in 1977:
This example was for sale on eBay, partially worked as you can see.
Below is a different example, the work finished, also from an auction.
I'm not sure where else you can buy RSN kits at the time when they are current apart from in their online shop; but they do have an online shop. Click on the link above to their site and follow the shop link to find it. Commemorative kits likely have a limited run and when they're sold out, they're gone.
The Royal School of Needlework has, of course, a long association with the royal family. Their most famous recent work being on Kate Middleton's wedding dress.