My Welshie is short and only takes a 4ft, the Masta sweet itch set fits with a bit of adjustment and a stitch here and there, he has a Rambo that is too big really. The one that fits him the best is the Snuggy Hood one, they start from 4'6 so his 4'0 had to be specially made
Try the Shetland Pony Tack Shop, Ruggles and Dinky rugs though as they will probably have very tiny ones