Yes, I've tried those sources. Dr Flue were most helpful, comparing the original firebox extenders to "hen's teeth" and mentioning that for a renovation project that they had to make their own.
Our model is a IMPDNo 1 (which doesn't mean much to me since we have only moved into the property with the coal stove, and I have had no experince of them in the past)
ok it sounds like a number one... i dont have any other suggestions on extenders.. do you realy need one?.. mine is number 0 which is a smaller version than yours.. i just cut the wood shorter.. also they run brilliantly on pine cones.