Have fun and just make it -
.......part bone a 8 1/2 lb turkey. Layer some stuffing over the insides, and fill the cavity with a 2 lb chicken, fully de-boned. Season well, and fill the cavity with 1 lb or so of boneless duck breast. Finally fill the remaining space with more stuffing so that there is no air space. Add somne fancy spices - cumin, paprika, cayenne etc plus a good load of herbs, fruit like cranberries, apricots, raisins - to jazz up the stuffing if you fancy.
Form the meat into a good shape - use your best 'guess' - cover and cook breast down first for 4 1/2 hrs or so in a med hot oven - 325 f / 170c, then finish for 1 hr breast up and uncovered to brown. Rest, carve & serve. Use a probe thermometer to make sure the internal temp is at 300f / 165c at least, so you know the thing is cooked through.......the above is a guide - I take no responsibility for making everyone ill cos you haven't cooked it properly!
A good butcher will make one up if you ask realllllllllly nice.