you can just buy a bung with a hole in it and fit a normal airlock or buy a fermrite vented bung.
any wineshop should have one or the other .
if your wine was dry when it went in the barrels its possible a wild mlf started and thats what produced the co2 and pressure
and your old 55 gallon barrels never went through mlf , so no pressure was created.
you should inoculate conduct full mlf , either before you barrel and only barrel stable wine or conduct mlf in the barrel under airlock .
if you did mlf , its possible it wasn't fully completed and came alive again when your free so2 levels dropped low enough.
once the wine is stable and sulfited a solid bung can go in.