It's a little bit intimidating when you've hit a brick wall and received no replies from RootsChatters except Ticker's list of sources. I've spotted some sites which contain more information about the National Archives of Ireland -
A Guide to the National Archives of Ireland - Internet Edition is one which I think will prove helpful to members who intend to call there to do some research in the hope of finding their ancestors.
Acquisitions from Private Sources The Public Record Office of Ireland, in an effort to repair as much of the losses of 1922 as possible, acquired records from many private sources, a policy which the National Archives has endeavoured to continue. These private sources have included business firms, solicitors' offices, trade unions, charities, estate offices and private individuals. From 1922-30 records acquired from private sources were referenced in a complicated scheme designed to replicate the pre-1922 arrangement of records under a large number of headings. From 1931-72 records have been referenced under a more simplified schemeThe above paragraph refers to Business Records.
In 1970, the Irish Manuscripts Commission initiated a survey of business records with the object of locating and reporting on collections in the Republic of Ireland and ensuring the preservation of material of historical interest. Since then, the survey has examined the records of over 5000 firms and other institutions and over 600 collections of records have been transferred for safekeeping to the National Archives, under whose aegis it now operates. There are 338 records in the subcategory
'Business Records Survey' on the National Archives website. I'm certain, if you don't succeed in finding the particular business in which you think your ancestor may have been employed an e-mail to the National Archives may result in you receiving a reply telling you whether they have records for that business. If your ancestors were employed in the six counties of Northern Ireland then send an e-mail to PRONI as they also have a collection of Business Records.