The Destroyer was an unequaled suit of arms not unlike that worn by the Celestials....
So I'm not even sure that it's Uru....
I don't recall it ever being mentioned at all and in a lot of the Marvel Bio's it says an unknown Armor....
So I wonder who first assumed or stated that it was Uru...because to my knowledge it has never been stated.
Do remember one of the Marvel handbooks stated that was made of Uri, that was then enchanted by Odin to be more durable, and to be ablke to reform even after blasted as Celestials did to it!