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 and Fallout: New Vegas. It covers the entire body. As such, it is impossible to wear a helmet or glasses with this armor, except the biker goggles.
Locations
It can be found deep within Vault 87, in the Test Labs. When you get to 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 you entered and turn left. That door is the storage room and contains the advanced radiation suit.
One can be found in the Citadel Armory. Most of the scientists found at Raven Rock will have this suit upon death, you can kill them without your Karma being affected as they are classed as "evil".
Another may be found in the Franklin Metro Utility, in a box titled "radiation suit case", at the bottom of a flooded tunnel.
One can also be found in Point Lookout, inside a muck hole during An Antique Land.
Another 2 are in Mothership Zeta, in the operating room in the Cryo Labs, on a table.
Can also be bought from Moira at Craterside Supply, Gustavo or Michael Masters from Tenpenny Tower, Karl at Meresti Metro Station, Tulip in the Underworld, Flak 'N Shrapnel's in Rivet City, Crow if you invest the maximum amount into his inventory and Knight Captain Durga in the Citadel if you get permission to trade.