for filename in $( find . -name '*.txt' ); do scp "$filename" hostname:~/ ; done

cd /Parent directory
    find . -name '*.txt' | cpio -pdm /pathtowhereyouwanttocopy

cpio copies files into an archive. It reads a list of filenames

find searches the directory tree rooted at each given file name

-pdm for overwrite destination content

rsync -vr --stats --progress --include="*/" --include "*.txt" --exclude='*' SOURCE DEST

scp username@Y:/path/to/directory/on/remote/machine /path/to/destination/on/X/local/machine

rsync -vr --stats --progress --include="*/" --include "*.txt" --exclude='*' username@Y:/path/to/directory/on/remote/machine /path/to/destination/on/X/local/machine