I'm not 100% certain but I suspect there are no direct flights Dublin/Crete.
I have done a lot of research into travel between the UK and Crete for my site http://www.travel.creteforyou.com
and there are no all-year-round direct flights.
During the summer holiday season there are many direct charter flights from airports all over the UK, including three carriers operating from Belfast in Northern Ireland, plus one scheduled route operated by GB Airways (a BA franchisee). In winter there are no direct flights, the most popular alternative route being via Athens.
If you're travelling in summer the easiest (and cheapest) option may be to get yourself to Belfast and use a charter from there. Lots of details and links on my site.