Already some year back (times fly) I wrote a post about using a spellchecker in Emacs on Windows. Today was a day when I needed to install spellchecker again, and found that OpenOffice dictionaries are no longer available on the link I posted. Now they seem to come only in form of extensions. Since I don’t find prospect of extracting particular dictionary form the extension file very appealing, I actually let Google do what it does best and found another link where language files can be downloaded. LibreOffice project has setup a Git page with all dictionaries, so it is just to get those you need. You can get them all by simply cloning repo:
git clone https://github.com/LibreOffice/dictionaries.git
Or just browse the link and get one(s) you need.