At the Rhein Centre, just across the border, there's a little India shop that sells them. Also you can try the Indian shop by Bahnhoff SBB (Walking away from the station, take first left after Burger King).
Bider and tanner have a brit food section which I think has PG tips but sadly not barry's. There are a bunch of Irish people here and someone is bound to be going home or having visitors.
have you been watching those nostalgic ads on RTE?