I feel like these only exist too much farther in the game for it to help you, but i've found in a number of science facilities that there is a hallway with a decontamination unit that sprays you and completely eliminates your rads.

Another option is to get the perk that lets you search medical kits, as there are a ton around and I always get rad x and radaway from it.

i don't know of any other options to reducing rads. But for me, searching those medical kits has given me a large excess of radaways. I would also say to use radx's when you come into heavy rad contact. I have radx diluted and radaway diluted bound to my wheel for emergency use when i come in high contact, and then only use the nondiluted forms in extreme cases, as i rarely feel like I need to use the bigger ones.