Memory Beta lays out the IDW collections status pretty well: http://memory-beta.wikia.com/wiki/IDW
All the minis up through Countdown
have been reprinted in trade, with the exceptions of The Last Generation
(coming in July) and The Hollow Crown
(will be reprinted with another Byrne Romulans mini, Schism
, once that completes). You can get them all pretty cheaply off Amazon.