Rodman sells the canned stuff.
But apart from that, I don't. (I don't buy it in a can, either.)
Ackroyd's bakery in Detroit sells it and will ship it to you. I haven't bought haggis from them, but I've bought pies and sausage rolls, and can confirm they are authentic.
https://ackroydsbakery.com/meats-puddings/haggis/