Sounds like a max size uploads issue in config of PHP/site.
One way around that could be ...
In the Moodle server to which you are trying to restore, turn on File System Repositories. Manually create a folder called 'restores' in moodledata/repository/. Set permissions for that folder where the web server user can see it.
Then create a category and a course called 'restores' - can be hidden if you like. No other users need be assigned to the course if you are System Admin. In that 'restores' course, create a file system repository that points to the 'restores' folder.
Using scp/sftp/ftpupload the larger than allowed .mbz backups to the moodledata/repository/restores/ folder - directory.
In the 'restores' course, use the restore link in the course admin menu to restore the courses from the repo to any other category you have created.
'spirit of sharing', Ken