I spent a good deal of time searching the net and chatting to people about this coin earlier this year and I could find no definite answer on the mintage numbers. The overall impression I got was that the central bank ordered around 750 coins in presentaion boxes from the royal mint. Some of these where in blue boxes but those were only given as special gifts to diplomats or senior civil servants involved in the UN. The rest were in cream coloured boxes, as in MasterSun's picture. Those were sold by the central bank to the public. But this was before they had a coin collector unit or a marketing department, so coin collectors didn't even know they existed. They would have been sold to whoever happened to notice them. In addition to the approximately 750 the central bank ordered from the Royal Mint, around another 2000 were minted for use in the 36 coin sets. But the sets were not very popular and very few were sold. So the remaining coins were sold off in capsules.
The royal mint have used various different colour presentation boxes for that size of coin over the years for many different coins and countries. So you can find all sorts of combinations of the UN coin and different coloured boxes that peolple have combined with the leftover coins. As Blade says there are two shades of blue boxes and I have also seen that coin in black, purple and green boxes, with and without certificates. And of course sold loose, with and without certificates.
Of course, the most desirable and rare version would be that in the correct blue box. But there were so few of them released and they were only given to dignitaries, so they are unlikely to turn up on the open market and if they did, very few people would know which was the correct box. I have met someone who has the correct combination and he knows it because he got it from someone who would have received one. And he says it is the only one he has ever seen.
So unless you have a friend who is a foreign diplomat or who represented Ireland in the UN, I think your best bet is to go for one in the cream coloured box. MasterSun bought his a few years ago for 120 (with a worn certificate). I bought mine this year for 200 (clean certificate). So you should be able to get one at the coin fair in October for around the 200 mark.
As for the 1997 mintage date. From the info MasterSun posted above it seems the coins were being released to collectors on a monthly basis to complete their sets. So I presume it wasn't our turn until late 1997.