Ireland isn’t selling bonds. But you can get a one year bond by buying a longer term bond that’s only got a year left. This would be via a broker not from the state itself.
One year seems to be trading at 5.11% right now.
My limited understanding is that these bonds tend to be sold in large amounts such as chunks of 100000e, your broker may expect 1% for his commission, probably at the buying end and selling end – so maybe 2%.
The tax will probably be a bit more complicated than DIRT, possibly a mixture of CGT and income tax.