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Are you in the US? I collect various species of Buddleia and that is one that I have never seen for sale anywhere. Why do you want it? I'm wondering if there might be another species that would have a similar characteristic that might be more readily obtainable (and I also noticed that the Wikipedia entry for it says that it has "minimal horticultural merit" so maybe it's not really a good garden plant--sometimes when you can't find something for sale anywhere there are good reasons why)
Since you posted this in Fragrant Gardening I'm going to guess you wanted it for scent? My favorite scented Buddleia is B. asiatica--its scent is reminiscent of freesia and I absolutely love it. I don't know where you are located though--it's not nearly as hardy as things like the B. davidii that everyone grows, it's only hardy to zone 8. http://davesgarden.com/guides/pf/go/2332/ I wouldn't recommend trying to keep it in a pot--I've had ones that I kept potted waiting for spots to open up in the garden and they lived, but didn't look very good and never bloomed. In the ground though they grow very large very quickly (mine'll easily hit ~10-12 ft in one season even if I cut it way back after bloom).
B. salviifolia is another nice scented one--somewhat reminiscent of lilacs. http://davesgarden.com/guides/pf/go/57953/ Also only hardy to zone 8 and in my experience not a good one for pots either. Also gets large, but not quite as vigorous a grower as B. asiatica. Both bloom in early spring on old wood so unlike B. davidii you have to be careful of when you prune them.
Ird...you don't have any info of where you are, (zone). Sorry don't know about the one you are looking for, but I do have another for you to look at that is also fragrant. Buddleia alternifolia, it's a spring bloomer, 8-10X8-10ft, Z5a-10b, lavender spring blooms, fragrant, common is Fountain Butterfly Bush, with arching branches, deer resistant, sun-p. shade. It's available from: Highcountrygardens.com, and they list it at 12'X8'.
I personnaly have seen this one in Denver at the Planetarium, a full grown speciman in full bloom and it was Gorgeous! I will have to put on my want list one of these days, lol... Kathy.
I had two Buddleia alternafolia at my previous house in Zone 5 (Ohio) in full sun behind my greenhouse. I would recommend that you plant them out in the open, rather than what I did. There really was not enough room for them. I found myself pruning frequently lots of small branches that did not have any leaves or flowers on them. When they bloomed, they got lots of comments. I also had Buddleia davidii which WAS planted out in the open and was extremely fragrant and had a beautiful purple color.