[Mrs. Don-o]

I looked and found out that the word "key" o "keys" is used just 4 times in Revelation, and in none of those is there any reference to 12 keys going to the Twelve.

Maybe in some other Book?

[BipolarBob]

I see what the problem is. You fail to understand the keys were symbolic of the powers given to them. They are not physical keys. The gates are real. The Apostles and their names are real. I'm not sure why you would be on a hunt for symbolic keys. If you are still confused then check out Romans 8:11 for further information.
At least the keys were mentioned which is more than we can say for a Pope position, a sinless Mary or Apostolic Succession.