Thanks to everyone from around the world who responded to my hissy fit - I have a whole slew of fallback options now including a Viking darning foot and the new one from the Janome 6600.
In the meantime, I remembered that just before I retired my 30 year old Kenmore, I bought it a gadget. It took a bit of rooting around in the studio but I found it and it turns out that the high shank BigFoot fits the Janome 6500 perfectly. They are even color co-ordinated. Huzzah, the weekend is saved.
My Goodman is eternally grateful that I am so easily amused. I miss you darlin'.