As far as I know this ONLY applies to water turtles and has never been applied to tortoises. Different states, cities and even counties have enacted their own rules and regulations now.
You can simply tell any seller at a show you are using it for educational purposes and purchase any size water turtle you want.
The original ban was to protect kids from getting salmonella, which is easy to get from poopy water.
Tortoise hatchlings are really quite easy to keep if you meet their lighting, heating and dietary requirements.