We know exactly for my grandfather and have an image of his birth record from the parish but no marriage record to Mama's mother (we only know her Christian name nothing else) or Mama's birth.
Can you prove that your grandfather and your mother didn't take up any other citizenship before 1962? Under the 1951 and 1920 Polish citizenship acts, that would have lost them their citizenship. Under the 2009 citizenship act lost citizenship can be reclaimed but only by the person who lost it.
all he has is his International Refugee Organisation travel papers that state born Poland but birth date and parents names are missing as he was an orphan.
That is going to be a problem; unless his parents have never been known, just being born in Poland did not make him Polish.
Because of the difficulties we face that is why a third party is under consideration.
Before you spend money there (or even talk to somebody who wants to charge you money to help you), you should firstly check with the Polish consulate in NZ what they think is needed. Also, check with them about your grandfather and mother taking up other citizenship(s). I'm pretty sure that there's something in the 1951 act about parents' decisions affecting their children if the children are minors.