Recipe calls for 4 ducks legs and 16 plums to be slow roasted. I got the duck legs but it's not exactly stone fruit season. Alternatives to plums that will be equally yummy?
Oranges. Duck a l'orange is classic and yummy
I think quince quarters would be nice, with a bit water (or wine, sherry, cider, stock) added along with them, since they won’t really release too much juice. Or how about orange slices (peel on, if you find thin-skinned, organic ones)?
Apples are lovely as well!
Figs and oranges together. Sweet and tart.
I was going to suggest quince, as lemon ade has. Also, if you have a well-stocked freezer or grocery store, look there...nowadays all kinds of fruit is frozen in peak condition. E.g. mangos or peaches would be great on duck.
Ducks with dates are delicious!
My mother used to make a delicious duck with grapes. Roasted grapes are lovely and I'd think they'd work well as a plum sub. Just make sure to use seedless.
I made duck alla porchetta for Thanksgiving and thought it turned out very well. The recipe called for duck breast, but you could adapt it for legs. Mark Bittman has a recipe and there are several others on the web. I took ideas from several recipes for my version.
I also think it might be interesting to do duck with pomegranate--you might google that idea and see where it leads.
my grandma makes this slow roasted duck with apples which I vaguely remember as very, very delicious.
Prunes would work well. They are dried plums. You could rename them to make it sound more elegant and less Grandpa-ish. :)