Ulster centre Trimble requires rehabilitation on a leg injury and will miss the Tests against the All Blacks and Wallabies on June 7 and 14.
D'Arcy was ruled out of the tour earlier in the week after undergoing further surgery on the broken arm sustained during the RBS 6 Nations.
The loss of Trimble and D'Arcy has left Ireland short on options in midfield with captain Brian O'Driscoll the only recognised centre.
Munster's Ian Dowling has been called up to plug the gap left by Trimble while Leinster rookie Luke Fitzgerald is also included in the final 30.
Interim Ireland coach Michael Bradley, who is overseeing the tour, has named a 37-strong squad for the clash with the Barbarians on May 27.
This will be reduced to a final party of 30 that will head Down Under, with the omitted seven players linking up with the 'A' squad for the Churchill Cup.
Munster's Heineken Cup final against Toulouse means their players will not be involved against the Barbarians but will join up with the touring party after the Kingsholm tune-up.
Bradley has opted against taking London Irish skipper Bob Casey to New Zealand, instead retaining Leinster veteran Malcolm O'Kelly with Alan Quinlan offering second row cover.
Bradley said: "New Zealand is a undoubtedly one of the most challenging places to tour and to win Test matches.
"After that we have a game against an Australian side that will have the fresh input of a new coach and are always among the top sides in the world.
"We are travelling on the tour with a strong squad conscious of the fact that IRB world ranking points are available and that is what we are playing for."
Ireland squad to face the Barbarians and for the summer tour to New Zealand and Australia:
Forwards: N Best (Ulster)*, R Best (Ulster), T Buckley (Munster), T Court (Ulster)*, B Casey (London Irish)*, R Caldwell (Ulster)*, S Ferris (Ulster)*, J Flannery (Munster), J Hayes (Munster), J Heaslip (Leinster), M Horan (Munster), B Jackman (Leinster), S Jennings (Leinster), D Leamy (Munster), D O'Callaghan (Munster), P O'Connell (Munster), M O'Driscoll (Munster), M O'Kelly (Leinster), A Quinlan (Munster), M Ross (Harlequins)*, D Wallace (Munster), B Young (Ulster).
Backs: T Bowe (Ulster), I Boss (Ulster), I Dowling (Munster), G Dempsey (Leinster), G Duffy (Connacht), L Fitzgerald (Leinster), S Horgan (Leinster), R Kearney (Leinster), G Murphy (Leicester), B O'Driscoll (Leinster, captain), R O'Gara (Munster), E Reddan (Wasps), J Sexton (Leinster)*, P Stringer (Munster), P Wallace (Ulster).
*Players for Barbarians match squad but will not be travelling to New Zealand and Australia.