Plants and seeds are widely available, you shouldn't have a problem. Not so rare. But be aware that they are fast-growing, wide-spreading trees, so need a lot of room. They also create a lot of shade. And the flowers are held high up, so it is best to plant it somewhere where you will have a good view of it from a location higher than where it is planted. I used to have one outside my 1st-storey window when I was a student in Oxford.