Ian,
You could probabaly get them at the Explorers garden in Pitlochry.They are difficult to get to a saleable size and keep them looking good, thats why they don't come cheap. Once you get a flowering size plant the best way to increase them is to scatter the seed directly into the ground, they prefer growing where they choose not where you want them.
Explorers Garden is free to SRGC members this Sunday and Julia also has her own garden open.
Susan