they all don't have the storage capacity ...... my local Asda stores don't have E5 , nor some of my Sainsbury's either and the likes of BP, well, last weekend I filled up with E5 and the difference in price was a staggering 14p a ltr rather than the usual 7p or 8p
The island of Ireland probably has some further limitations with storage and volumes of types of fuel being sold too
Good luck with it all .... my E5 garages i now know locally here in my part of Kent
Malc