I have my Christmas ferns (Polystichum acrostichoides) in shade, but they're supposed to be more sun-tolerant than many ferns. They have a somewhat different look than ostrich ferns, but I like it, and like the fact that the foliage remains through the winter.

Well I would first suggest making some shade if at all possible, with a trellis or a statue or a garbage can or something. Or a shrub or tree. But failing that, I've grown a number of Dryopteris ferns in quite a bit of sun, though mine always got some relief in the afternoon which is when yours will be exposed. Having said all that, there isn't much I'd put past the Robust male fern, Dryopteris x complexa.

If given lots of water, Osmundas grow quite nicely in the sun. Try both O. regalis and O. cinnamomea. But remember to keep them very moist (or even wet) or they will dry to a crisp! PF

I've found Hay-scented ferns (Dennstaedtia punctilobula) equally hardy (and beautiful!) in both sun and shade -- and they spread rapidly. As someone else noted, the Ostrich ferns will be fine in the sun if they have adequate moisture, BUT even so, they'll start looking sun-burned and tattered in late August, whereas in a shadier spot they'll be green and attractive right through the fall.

I think the suggestion of making an arbor for some quick shade is great. Cover it with an annual that grows quickly to start and then plant some perennials that will eventually take over. I made one with treated wood salvaged from an old deck using 2 6"x6" posts set in cement, nailed a pair of 1x6's-one on each side-and then using short one by ones accross them for a real substantial structure. Cutting the ends at an angle gave it a nice finnished look. If you put some lattice with it you'd get a nice patch of shade.