Welcome to the Bunnings Workshop community. It's wonderful to have you join us, and thank you for sharing your question about boat building timbers.
The common ones available at the store are pine, teak, and spotted gum. Other timber types might need to be specially ordered if you're after a particular species of wood. But among those, pine has the largest amount of variety where size is concerned.
Are you planning on building a boat? Did you make a design yourself or did you find a plan online? If you decide to proceed with this project, any photo updates you can provide would be greatly appreciated. I'm sure our members would be very keen to see your project.