Jars of Vegemite are available in Superquinn, Swords. Perhaps Vegemite is available in this supermarket chain nationwide. I purchase a jar (with my groceries) every month or so. It would not be wrong to say that I do a good bit of the family shopping at this supermarket because I can purchase Vegemite there.
Vegemite is a yeast extract. It is darker than marmite and has a far sharper and more salty taste. Some people describe Marmite as much blander. I believe Marmite originated in Britain; whilst Vegemite was developed in Australia between the first and second world wars.
One slice of toast with generous spread of Vegemite is, for me, a good weekday breakfast. I know one particular person who, for many years, swore by vegemite and cheese sandwiches. There are many, many combinations, most of which might sound very unpalatable.
Vegemite is ....an acquired taste.