You could use static data for that. Here an earlier post about that in the forum:
and here the docs:
But as documented it is only meant for small amounts of data. So I would advise to only save a hash of the site map and not the full one.
If you really want to save the full one, it is probably best to save the sitemap either as a file on the hard drive with the File-Nodes or in a database like Mongo, Postgres, Redis.