Dehydrated butter (in #10 cans) is a very common thing to find in the pantries and storage rooms of 'preppers' (me included). It really is not useful for putting on toast (and honestly I wouldn't even try to 'rehydrate' it the way one might a peanut butter powder) but it works well for baking (and sauces too). Haven't tried the ones from the supplier you mentioned, ElsieD, but I have bought several cans in the US from Emergency Essentials and similar places. They do vary in quality however - so if you are in the market for some, I suggest you do some research first to see what 'preppers' say about a particular brand.
I see HoosierHill's powdered butter only stores short term (in my opinion - about a year) but that is probably because of the packaging more than anything - and is GMO free which is good but those things are also reflected in the price which I think is fairly high compared to others on the market (which may not be identified as GMO-free mind you).
For butter that will store fairly long term but will be great on toast, etc., go for Red Feathers canned butter (which is real butter, not dehydrated).
