Nope, not illegal to buy them, but did think it's something people who are interested in getting a turtle should be aware of.
My grandpa never put uv lights on his turtle, but he put her outside when he cleaned the tank, if the weather allowed for it. I'm not exactly sure how to calculate it, but there's a lot more uv in sunlight than lamps. A few minutes in the sun will suffice for uv lighting, but if you don't live in a climate where you could do this on weekly basis most of the year, this probably isn't an option for you.