I had never seen one, just knew that there was such a thing. I found one on Etsy; the complete set, with the throat plate, the bobbin cover and the guide finger. As soon as I saw it, I knew that it wouldn't work-the throat plate is wrong.
I think my confusion comes from the fact that I knew that at least one of the 400 series could do a chain stitch, but ISMACS says it's the 411.
WRT chain stitching-some machines (notably the Touch & Sews, apparently) came with an attachment set that would make a chain stitch. I've seen them used for both embroidery and for making slopers and muslins.