I have had my tailors dummy for about ten years now. As you can see above, I have covered it in trims in shades of white, cream and aqua that I have collected over the years from antique markets and haberdasheries. Recently, I was asked on Flickr where to get one from.
I suggested Baileys home because they sell a variety of vintage tailors dummies and I think the mix of old and new in their store is just right.
On further investigation, I found this great dummy upholstered in vintage Russian linen from Ghost furniture.
On the other hand, if you're looking for a something a bit more special, then I suggest taking a look at Corset Laced Mannequins, who also make bespoke dummies in any suitable fabric you provide.