Register official Nintendo controllers/accessories on Club Nintendo

Right now, none of your coins are going to expire.

Basically, how it works is you have 2 Club Nintendo years (July 1 to the following June 30) to use coins you have gotten from registering games and doing surveys, etc.

What this means is, if you were to register a game today, you would have 2 CN years from TODAY to use them.

If you registered a game a year ago, you have one more CN year to use them.

It is basically a floating window of time based upon whenever you registered the game.

The game should have come with a leaflet that has the code on the back. You're not completely out of luck though, because I found this in the FAQs on the Club Nintendo website:

My Game Didn't Come With a PIN Code. How Can I Register My Game?

Answer:

If the game you purchased is eligible for registration and the card with the PIN code is missing, please contact us and provide your name, username, email address, and the game title you're inquiring about.

That question is on the North American Club Nintendo. You can select 'Other' > 'UK & Ireland' for your country, but if you're using the UK Club Nintendo website you should contact support with this form.