If it's a 144 BCD crank, you could get a triplizer. It's a special middle chainring that will allow you to add a 3rd, small ring. You may need a long cage rear derailleur and longer spindle. The company is Red Clover Components and the owner is a member here if I'm not mistaken.

Edit: Ok, it's a 130mm BCD according to RHM and velobase. You can get a triplizer from France for a 130mm BCD also: XXcycle - Plateau Stronglight Intermediaire porteur triple 130/74 - en. Basically, there are lots of options to change the gearing. Some options will allow you to keep the bike more period correct and others will allow you to emphasize function using more modern parts.