You can get aluminium solder. However I have found it is very hard to use too little heat and it just blobs, too much heat and it will collapse. I tried various gases propane, MAP, oxy acetylene. Oxy acetylene worked best however I would find an old stuffed aluminium core from a car, motorcycle wrecker, or scrap dealer and practice and practice. Only when you can do it successfully and consistently would I the tackle the Brick radiator. Critical to getting a good repair, is the area you are cleaning must be extremely clean. I used a new stainless steel brush and weak acid. Googling You Tube for aluminium solder techniques will help. If you don't have any radiator repair places a good welding shop might be able to help you.
Good Luck Regards Martin.
