Sources of plants and seed for triggerplants vary a lot by geographic region. Be sure to check and follow local import regulations.
There are some posts and links at the ICPS Forum which may help you find sources. Go to the website of the International Carnivorous Plant Society and follow the links to the forum. Other forums which deal with carnivorous plants may also have useful links.
In Europe and Asia, it may be best to check with local carnivorous plant enthusiasts who may have plants or seed for sale or trade. Chiltern Garden seeds often has a few species.
In Australia, Allen Lowrie's seedlist is just about the only place to find lots of tropical species, along with many temperate ones. Wildseed Tasmania usually carries Stylidium graminifolium. Nindethana Seed Service usually has a number of species of both Stylidium and Levenhookia. Other useful links might be found at ASGAP.
In the USA, try the webmaster for seeds and plants, and J. L. Hudson also sometimes has one or two species.