Is there away to seal paper mache clay items to be put outside?

Mod podge or clear painspray

A marine grade varnish or shellac.

I just finished hanging "Cleo" my paper mache flying pig! After painting it I sprayed several coats of "Helmsman" spar urethane. I've used this product before & it has worked well!

A marine varnish or several coats of a good oil based urethane. make sure you get the non-yellowing kind of marine varnish.

Several coats of polyurethane should work. Since they are going to be displayed outside on top of a table, had you thought about spraying them with polyurethane several times and then putting them under a cloche, of some sort? It would look wonderful and protect them from the elements a bit.