After searching around a bit for appropriate 25mm-28mm dogs, I settled on one of two canines contained in MIRLITON MINIATURES' "Medieval Accessories" range. This is a very useful range filled with all sorts of odds and ends, including farm animals, draught oxen, furnishings and Medieval architectural details, as well as several sets of Medieval civilian figures. Though most useful for Medieval purposes, the animals and some of the accessories have far wider usefulness.
I used the dog on the extreme RIGHT for Bobbie. The miniature is actually a slightly larger dog than the real Bobbie was but nonetheless, in my opinion he is the closest resemblance I could find. Plus he's just a nice figure...
Here's a link to page 3 of the 5 page Medieval Accessories range, where you'll find Bobbie about halfway down the page, as part of pack AC084 - "Dogs and cat"...
Mirliton Medieval Accessories
