Hi,
You need to contact the pensions dept in your hospital. They will calculate the amount it will cost to buy back the missing time. You then have the choice to pay it in one go or to have it deducted from salary over a period of years.
Cornmarket only deal with the AVCs, the HSE deal with buying back years or purchase of notional service. Just be aware that purchase of notional service can be quite expensive (I was quoted between 10k and 20k per year purchased).