If you would like to order a wreath for Armistice Day or Remembrance Sunday, you can do so by contacting the Royal British Legion directly: https://www.britishlegion.org.uk/get-involved/ways-to-give/shop/wreaths
They are able to provide a portcullis badge for the centre of the wreath, but you will need to request this at the time you order the wreath, and only ‘Type C’ and ‘Type G’ wreaths can accommodate a central badge. You have to order by telephone if you want the House of Commons badge because it’s not on the website: 0345 845 1945.
You can order wreaths at any time of year but, obviously, they are busiest in October and November, so do try to order in good time. They suggest that orders for Armistice Day should be placed before 24 October.