Find black cocoa powder (a.k.a. black onyx cocoa powder) in the UK

"Ramen noodles" are a predominantly North American term for what the Japanese call "Chinese Noodles" (Chukamen, which I've also seen spelled Yuukamen).

In practice, you can use any wheat noodle that's made with eggs or kansui, including lamian or mee pok, or even buckwheat noodles (notably soba). Noodles made without either of those are not recommended.

It does not matter which of the above you use, although the Chukamen varieties are the more traditional. Much like pasta, it's largely a matter of personal preferences and how you want it to come out in terms of texture and appearance.

You'll find a wide variety of all of these noodles in dried or fresh form at any Asian supermarket or grocery store. Across Canada there's a chain called T&T. You should have no trouble finding some Asian grocery stores in your region with a phone book or maybe Google or Yelp.

Store cocoa powder in a dark, cool, dry place, sealed against vermin. Dark and cool both slow the process by which volatiles (i.e., flavor) degrade. That said, don't keep it in the fridge or freezer unless sealed airtight, because both types of chill-chests are relatively humid environments. Humidity promotes mold, even on cocoa.

By the way, for future reference: When buying cocoa powder, note the manufacturer's suggested use-by date. Cocoa powder should last about three years, properly stored. If the use-by date is much less than that, look for another container.