I know they do grow big. We used to have a 2.5 metre high natal bougainvillea hedge in our garden. And in durban and the areas around there are some huges ones. I have looked on the internet and found that this particular species is a more compact growing shrub, which now begs the question is this really a suitable specimen for Bonsai. I can't find any pictures of the " Tom Thumb Bougainvillea " having grown big. In South Africa the variety of bougainvillea is huge. On the Malanseuns web site (
http://www.malanseuns.co.za/List.asp?MainCat=Trees%20and%20Shrubs%20/%20Bome%20en%20Struike&Cat=Bougainvillea ) there are a few species to have a look at. Some of it is afrikaans so you may not understand. But there are a number of pics. And the Tom Tumb is said to be approx. 50cm X 50cm. Have a look and let me know what you think. PS. Thanks for your comments and have you had a look at my other post?