I personally don't like third party couriers as I don't like wondering who has our/their birds or using holding pens/lofts. It is just a personal preference and nothing against couriers that do and wish them all the best
It keeps away some bugs and moths from the nests and lofts, it makes great nesting material and it smells lovely in the loft a lot better smelling than tobacco stalks
I have never seen them for sale, if you know anyone that has lavender the bushes die back at this time of the year and they are happy to get them pruned if the don't use them themselves