1st, ASFs are illegal in California, so it is very unlikely that you will find them.
Other than that, when a snake starts eating and is fine for a time and then begins refusing husbandry is almost always to blame. You said that the snake ate for your cousin, but then you got him and he has not eaten since. From this you know that the snake knows how to eat, so you have to ask yourself what is different and fix it before you go force feeding and such. What are your husbandry practices? What kind/how big is the viv? What are the temperatures? Hot side, cool side, measured with what? How is the humidity? Does the snake have a lot of places to hide or is it out in the open?
Let's figure that stuff out and get the snake eating on it's own again. Force feeding is really stressful for the animal and should only be done as a last resort for animals that are either ill or have never taken a meal on their own.