It would be overkill for your purposes, but the one I have used is an
ITW Plexus epoxy-type resin specially formulated for aluminium
http://www.itwplexus.co.uk/

This was through the product reps that gave us a chance to try out
several of the products - and then test the joints to destruction.

Simple lap joint in aluminium sheet - the aluminium fails before the
joint.

Probably best bet for small quantities is a yacht chandler.