You can buy these through Davy Stockbrokers.
Commission is 0.5% plus €40 custody charge plus an annual holding fee of €7.50 per holding (plus VAT) with a minimum of €45.00+VAT ie €54.45
I have purchased €50,000 in the past so it is possible. If buying, remember to buy Benchmark bonds as the dealing spread on these is a lot less than the spread on non-benchmark bonds. They will quote you a market price.
I don't think it is easy or possible for a retial investor to purchase bonds directly when they are issued, so you have to pass by a broker.
Irsh gov't bonds are also available from broker in the UK, but do not know about minimum amoutns nor fees