Use lots of green in your decorating efforts. Green bows tied around big vases of flowers. For this look I usually use the old spaghetti jars..they look fabulous as they are so tall.
Can you get hold of green plates and napkins? Even paper plates and napkins could serve - not as swish but you would probably find the getting of the green napiery easier.
Serve a lot of green type food maybe include foods such as asparagus with homemade mayonnaise, green jelly, mint cocktails - you get my drift...
Get your guests to wear something green or even all green clothing. Would you be game enough to put a big green (but temporary) streak in your hair?
Play the good old Irish songs and music such as "O Danny Boy" "Take Me Home Again Kathleen" etc..
Better still if you can manage to get the words to these songs then have your guests sing-a-long to the songs.. ...cheers
ps hope this helped.