When you layout the ribs for the wing tube & socket holes, make the holes oversize. You can then cut "washers from plywood that are a good fit to the tube & socket. Then when you put the wing sections together, & line them up, just glue the "washers" to rib in the exact location the socket & tube fits.
Aluminium tubes and sockets are available from TNT : http://www.tntlandinggear.com/
and Gator R/C: http://www.gatorrc.com/