Any oil will work if you do not have avocado oil, I would use olive in its place.
You could sub the beef for turkey as well, but your gravy might not thicken as easily without the extra fat from the meat.
You can use gluten free soy sauce or tamari if you do not have coconut aminos.
Any starch can be used in place of the tapioca, such as corn, potato or arrowroot.
For the sour cream I like the Follow Your Heart brand for dairy free, or the Green Valley lactose free.