Try the Midleton Destillery and ask for advice, they have a barrel maker mending their barrels. So I suppose they would be able to help you with a material suply question. A basket weaver could put a ring made of wicker around the barrel instead of steel, if you find one still in the trade.
A timber barrel should always be kept filled to stop the timber from shrinking. Maybe keeping it topped up for a couple of weeks will close the gaps, these could also be filled with leaves of reed compacted into the gaps.