The advanced radiation suit is a suit specially designed to protect the wearer from harmful radiation, and to a greater extent than the standard radiation suit, meaning it has greater radiation resistance than any other armor or clothing in Fallout 3. It covers the entire body. As such, it is impossible to wear a helmet or glasses with this armor, except for the biker goggles.
It can be found deep within Vault 87, in the Test Labs. In the room with the Lab Technician's terminal (on a desk to the right), one of the options will be to unlock the storage room. Choose that option, then turn around and go back out the door that led into the room and turn left. That door is the storage room and contains the advanced radiation suit.
One can be found in the Citadel Armory.
Another may be found in the Franklin Metro Utility, in a box named "Radiation suit case", at the bottom of a flooded tunnel.