If you are just starting out, I can thoroughly recommend www.rubbadubbadoo.com. They have a huge selection of very reasonably priced stamps available mounted and unmounted.
In my very first ‘dragonfly phase’ I didn’t even have the stamps yet – I photocopied the image from the Rubbadubbadoo catalogue, coloured in the wings with coloured pencils and used Kindy Glitz on the bodies to give a bit of sparkle. I cut them out and stuck them on everything.
Later I bought a set of dragonfly stickers from the Fox Collection www.foxcollection.innovations.co.nz. They were gold and you could colour in the spaces.
Now dragonflies appear regularly in a whole heap of different guises.