There are also oak chips, dust, and spirals that most homebrew shops and websites carry. My reservation would be that it can be easy to over oak a product. Good thing some brands are widely available and "affordable" for experimentation. If you over oak something like a widely available blanche or verte that's fairly consistent in flavoring, one could probably get by with blending it with a fresh bottle. It wouldn't be a bad experiment to throw at a guest being introduced to absinthe who might be coming from more of a whisky, brandy, or other oaked spirit background.
I've only oaked a few homebrew experiments, but if I were to use oak chips on an absinthe, I'd probably start with a blanche.