The Irish broadside trade (referred to as 'ballads' here) carried on until the mid 1950s, one of the last sheets reported being a parody of Slim Dusty's 'Pub With With no Beer' (re-named 'Bar With No Stout'). The main participants in the trade were Travellers - there's a beautiful description of one of the Travellers we recorded (teaching a tune to a prospective buyer) on our Musical Traditions CD of field recordings 'From Puck To Appleby'.
The speaker, Mikeen McCarthy gave us a load of information on the trade, which he and his mother were part of in the early fifties.
An article entitled Michael McCarthy, Singer and Ballad Seller' was included in the collection of essays, 'Singer Song and Scholar' edited by Ian Russell (Sheffield Academic Press - 1986). Anybody who wants a copy of the article can PM me.
Jim Carroll