For that I’d say something like “Táim ag lorg poist”, or “táim ag iarraidh post a fháil.”
Keep in mind that when translating, you should really seek to boil down the essence of the *meaning* you’re trying to convey and not attempt to do things word for word. This is actually challenging, but it’s generally a skill that’s very much worth cultivating. In other words, not all statements that begin in English with “I’m trying” or “I try” will begin the same way in Irish (or any other language for that matter).