Ancestry.com has a digitized collection of New York metropolitan area city directories for that era and a search of them comes up with many "hits" for the name LaFrance. Your local library probably has a subscription to Ancestry.com (or similar database) and if no answer appears here, perhaps you'll want to drop by and spend some hours looking through all the possibilities.
One could also check classified ads and newspaper references to the business, but of course the word LaFrance might not be part of the business name,and I agree with you that a city directory is a better bet.
Chronicling America is a Library of Congress, public, free, database that includes a collection of digitized New York City newspapers of the era:http://chroniclingamerica.loc.gov/search/pages/results/?stat...
Another option would be for you to share more information about your project and see if that helps someone to help you.
Hope you find your answer. Happy hunting!