I do have to laugh when I read that you have to replace a 53t chainring and a 12-21 cassette. That is pretty serious riding.
You can find Shimano SG B-53 130mm 9 speed chainrings on eBay. Either a 6500 or 5501/02 should be the same.
The cassette is up to you. I doubt you will find a 12-21 9 speed cassette. But you can get a Sunrace, SRAM, Shimano 11-25. Since 9 speed is not as popular as it used to be, there is a very small market for a 9 speed with a 21t or 23t large cog.
I like KMC chains, but SRAM or Shimano are fine. Make sure you get one with a master link.
You might want to add cables and housings to your list. Last thing you need is to get there and find old and/or frayed cables.
Maybe brake pads???
John