How to discover the passwords for the Sonic Generations secret trophy room?

Question

There is a secret trophy room in Sonic Generations.

Hold down Select or Back button while inside the Collection Room.

Once inside the trophy room, trophies are unlocked by inputting 6-digit codes.

How can players discover such codes by their own?

I'm not interested in a list of the codes. I know I can search the web and find such list, but doing so spoils all the fun. What I want to know is how can I discover such codes by myself. Does the game give some hints about the codes? Did SEGA release hints somewhere outside the game?

Answer 1

So, from the looks of it, these are not unlocked in the game. Rather, as The Sonic Stadium blog states (warning some codes are listed, avert your eyes):

According to Hogfather on the SSMB, the codes are printed on particular merchandise tags e.g. on T-Shirts and pants tags.

Also:

If you haven’t already scoured the internet to get the hacked codes (because that’s cheating, isn’t it?), then don’t worry, because the Japanese Generations site has begun to give out some of these codes!

Looks like these codes are rewards for buying merchandise (or looking them up online).

Also, as a update, it looks like the official SEGA blog is also releasing these codes.