I bought it at an exhibition, I think the trader's name might have been something like hobby holidays, but when I searched online, it didn't seem to be the right one. It was sold as 7mm scale fine granite, but having compared it with what's on the Midland main line, yesterday, I'd say it's exactly like gauge 3 scale modern granite ballast. Really far too good for Great Eastern branch lines. I bought one 1Kg bag, spread it on the layout, and worked out how much more I'd need. Postage is a bit of a problem, I was fortunate in being able to carry the rest home on the train, in a rucksack.
Having seen your address, I suggest you browse what gaugemaster have in their shop, to give you some idea of what's available.
I think I mentioned earlier that I built up the trackbed around the sleepers with balsa wood, to minimise the amount of ballast needed, and reduce the weight of the layout.
If you're modelling track where the ballast covers the sleepers, Cliff barkers track can be laid without sleepers; you can fix the rails down using the pegs supplied with the chairs, drilling holes in the track base.