How can you extract private keys from MultiBit HD? It was possible in MultiBit Classic, but I can't find it in MultiBit HD.
WARNING: While this answer may be a solution to the issue in the question, it involves exposing your wallet seed to a tool on the internet. Please be very careful when doing this!



Can't add comments so extend Chris.J's answer:

Here are my notes on how to recover / rebuild / regenerate / extract ALL addresses and keys used by MultiBit HD:


Go to https://iancoleman.github.io/bip39/
In the field "BIP39 Mnemonic" fill in your 12 wallet generation words
No password
Code: Bitcoin
Under Derivation Path, select the BIP32 tab
Client: Custom derivation path
Derivation path FOR EXTERNAL (RECEIVING) ADDRESSES (copy paste this): m/0'/0
Your receiving addresses are now displayed at the end of the page. 
Derivation path FOR INTERNAL (CHANGE) ADDRESSES (copy paste this): m/0'/1
Your change addresses are now displayed at the end of the page. 
Absolute Happiness ;)


(solution found on:https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki in "Hierarchical Deterministic Wallets" picture)