Where can I download the game? all that is coming up is PlatinumQuest

PlatinumQuest includes Marble Blast Platinum as well as Marble Blast Gold. you can run platinum through platinumquest considering it is the latest build of MBP but only MBG requires the original build due to slight marble size differences.

You can download the game by going to https://marbleblast.com/index.php/downloads/pq and then selecting the version you wish to download - either Windows or Mac.