If you can't get Nutracal or Nutrastat, see if the pet store has any other kind of nutritional supplement, just to have on hand if he won't eat or gets ill. Corn syrup is another option in an emergency if you see him shaking.
While you are at the store

get some plain yogurt and or cottage cheese.
and boil some chicken and make some rice
Try to keep him on the food the breeder had him on, but if he won't eat you will have options. When I brought Shelby home my kitchen looked like a chemistry lab. I tried everything but she lived on kibble dipped in nutracal for quite a while.
good luck.