I'm intrigued myself, and sent off an email to my favorite nursery/local nursery to see if they knew a better place to find some.. I've never heard of these of the outfits in those links, myself.. Maybe someone else here has?
I don't think I ever considered where sloe gin came from so I looked it up. Turns out there is a Sloe berry. Here's a recipe from the BBC Looks pretty easy of you can get the berries