If you really just need all possible spellings, then I would suggest downloading Google N-Grams for N=1 (single words). These are individual words/strings coming from books in the French language. You also have the year, the count in that book, and the part of speech, if available. From this data you can create frequency lists of all unique spellings.
The individual files are quite large. For example, a single file,
googlebooks-fre-all-1gram-20120701-a.gz is 194 MB compressed, and 1.0 GB uncompressed. All full of single words.
The structure is quite simple
ngram TAB year TAB match_count TAB volume_count NEWLINE
So an actual line in the 1-gram files will look like this:
âutre_ADJ 1794 1 1
where _ADJ defines the part of speech.
License is Creative Commons Attribution 3.0 Unported.
p.s. I'm a big fan of Python's Collections library for the task of counting frequency of something too large to read at once. See here for example of counting characters. There is also a Python N-gram downloader package, but in this case I prefer to get the files manually (since they are needed to be downloaded only once).