There is a Eurail Aid office in Dublin Connolly station:

https://www.eurail.com/en/get-inspired/trains-europe/useful-train-information/eurail-aid-offices

I'm not sure however if they can also sell Eurail passes. It's probably best to ask Irish Rail directly.

Irish Rail do not sell Eurail/Interrail tickets and haven’t done so for a long time.

If you cannot get a Eurail pass there are some other options, they may even be cheaper or suit your plans better anyway.

Irish Rail do sell their own tourist oriented tickets. A 4 day consecutive for €110 and a 5 day out of 15 days for €160

These offer unlimited use for the relevant days but are only for trains in Republic of Ireland, not Northern Ireland. These tickets can be bought at any staffed station.

https://www.irishrail.ie/en-ie/rail-fares-and-tickets/tickets-explained#Tourist%20Tickets

A day ticket for Northern Ireland costs £16.50 and covers all Rail, Bus and Coach services in NI which are run by Translink. This is offered on a smartcard that can be bought online and posted to you or bought at main bus and rail stations, The card can be loaded with as many day tickets as you wish at any time. They only become active on first use at a station or on a bus.

https://www.translink.co.uk/usingtranslink/ticketsandtravelcards/ilink

Also of possible use is the Leap Card for public transport use in the Dublin region. A Visitor Leap card is offered that gives unlimited use on Bus, Tram and Train for €8 per day or €16 for a 3 day ticket.

These can be ordered online to be posted to or bought at a small number of places in Dublin including at Dublin Airport.

https://about.leapcard.ie/leap-visitor-card