Ask Lon about the Finns that are still to be cast. They have never been released and I keep requesting for this to happen.
The Battle Honours will fit in, but be aware they are getting on in years.
In no particular order, Force of Arms (FOA are away for the year, however, Hall of Heroes can provide), AGN, JTFM, Company B and Warlords all have something in their arsenal for the conflict.
If you check my older threads you will find a number of references to the Winter War.
You will find that Warlord games are in the midst of revamping their WW2 ranges so patience is required. I know that it doesn't answer the question, but perhaps an e-mail to Paul @ Warlord Games might.
Cheers,
Helen