Aluminum isn't so bad... I weld it all the time, a Radiator (presume it is a tank that needs patched no the core?) will be pretty thin material... a skilled user could MIG it with a spoolgun and 4043 wire... Stainless is not horrible to weld either. I do that less often but it welds like a dream once you learn what you are doing same with alu...
I'm in Kansas City, West bottoms area if you want to bring it by I can take a look...
if it is the core that needs patched then you would likely be better off and money ahead to just buy a new radiator...