Toslti they're Pork sausages from Yorkies on Soi Chaiyapruek. I think you can get them in frozen form at Friendship and a few other local supermarkets, but I always go to their shop and buy them fresh.
I don't eat a lot of heart-attack on a plate food these days but when I do, it had better be good. And those bangers taste as good as they look, trust me. Not exxy either, about 200 Baht per half dozen.