I have spoken with a GM about this, below is the reply:
I’m Game Master Larissooquie, I hope your day is going well!
I know you’ve been waiting a lot longer than is ideal for a reply so your patience has been very much appreciated.
You are right, players who pre-purchase Warcraft III: Reforged will receive Reign of Chaos and The Frozen Throne cd-keys as a bonus.
The bonus cd-keys will be delivered sometime after the original purchase, however, at this time, we do not have a timeframe for when the classic keys will be delivered,
I hope this clarified the issue for you.
As far as I’m aware, there is currently no way to purchase the original game on the blizzard store, yet 3 days ago I could have purchased cd keys for wc3 and the frozen throne for £9 each and be playing them now.
How is it that these cd keys no longer exist? Can it really be that difficult to create and distribute them for people who have preordered WC3: reforged?