Hi Light,
Do you know if they were Protestants or Catholics? Civil registration for Protestants began in 1845, which might just be early enough, given Bernard's birth date. If they were Catholics, however, you'll need to look for a parish register, since they weren't included in civil registration until 1864, by which time your family were already in England. Tracking down the right parish (and possibly the right townland) may be difficult if all you know is the county.
My Irish ancestors were all Catholics from SW Cork (where nothing is online yet), and I don't what records are available for Co. Roscommon. You might want to try
GENUKI's Roscommon page as a starting point, or just start Googling.
Good luck -
Tim