There does not appear to be a Jobo distributor in Ireland so probably your best bet is either the UK (www.novadarkroom.com) or a Euro-zone country if you prefer to deal in Euros... The red caps are only 4 quid in the UK. Postage will cost more than that, so try a local dealer first - they may be able to order one if they do not stock it.
Should be a normal spare part. You'll likely get the whole lid without the insert. Make sure you get the rubber cap to. Then remove the insert from the lid you have and put it into the new lid. If you want to use both lids without changing inserts then order one to. Either the film or paper cup.