Avgas is available in Denpasar, Ujung Pandang/Makassar, Balikpapan, Samarinda. From Samarinda/Balikpapan you can go to Tawau in Malaysia and then onto Phil... but I am not sure if Avgas is available in Tawau. They are in Kinabalu.
You need to call ahead on those airports about avgas situation.
Alternative route is from Balikpapan you go to Manado if your plane can hop that far.
Avoid Ambon, Palu or Kendari... stick to those airports mentioned above and you'll be safe.
Avgas is abundant in Balikpapan and Samarinda. the rest, you need to call ahead.
Go to
www.angkasapura1.co.id and
www.angkasapura2.co.id to get details of the airports you need along the route.
PK-KAR