I don't know what you're calling standard flux and solder (though this
brings to mind the various tin/lead or modern lead free types of solders
suitable for yellow metals, tins and steel). There is aluminum solder
which can be used for aluminum and works quite well with some practice.
The process is closer to welding with what I've used and these soldering
rods are available at many welding suppliers, automotive and farm
mechanical supply places. Bus bars I've seen were usually Aluminum,
brass or plated brass. What sort of process do you anticipate - just
curious.

wrote:

recommend a retail source or recycled source of 1xxx aluminum that is
solderable with standard flux and solder?

a suggestion was bus bars-are bus bars solderable?