i got one from tesco lol but it does slip around abit not sure they would have the size you would want but they seem quite wide at the chest (i always have problems with rugs being too small around the chest) and the neck cover is very wide i guess it depends on the quality you want mine seems to be doing the job look on their website nothing ventured nothing gained
At the moment Premier Equine are selling their Sweet Itch Buster at half price. I bought one & they are generously sized, their largest being 6'09". They are very hard wearing, There are others for sale on their site as well....her's the link
id recommend the bucas fly rug- its got a really wiide chest and a belly flap which is great.
its quite pricey at 80 odd quid but well worth it.
personally i found that the weatherbeeta ones slip. alot.