* NordLB looking for about 3 billion in fresh capital -sources. : FRANKFURT (Reuters) - Commerzbank (CBKG.DE) has made a non-binding offer to take a stake in German NordLB, people close to the matter said, as an auction for the ailing public-sector lender progresses. NordLB aims to boost its capital by about 3 billion euros ($3.4 billion) to cope with bad ship loans and has asked for final bids by the end of November. Public-sector peer Helaba as well as private equity investors Apollo, Cerberus and Advent also handed in tentative bids earlier this month.