Couldn't some other countries donate the wood necessary to rebuild the roof if France does not have the requisite number of trees?
Given modern forestry practices, the only oaks likely to be of the requisite size to rebuild the roof exactly as it was will be in protected areas. There also isn't any other tree suited to the task than an oak. Those that produce wood of sufficient strength don't produce beams the size of those that were in Notre Dame.
It would be possible to plant oaks and let them grow to the requisite size and age, but I think we don't want to wait until the 23rd or 24th century to rebuild the roof.