Before you start working on an aircraft
... read through these chapters about aircraft hardware.
Replacing the old hardware while working on the airplane is the cheapest way to get new parts onto your aircraft. New bolts and nuts are plated and resist corrosion better than your old pitted bolts.
Download the file to print: About aircraft hardware , 1.3 MB PDF file
Substituting parts for older aircraft is regulated. Follow this link to read what can legally be done - be it owner produced or PMAd parts.