I wouldn't recommend it, but if you choose to do it, I would only do it under your doctor's care. When I was pregnant with my first, I was dilated to 4cm already and having contractions at 38 weeks, but the contractions weren't getting much closer. My midwife suggested castor oil and I was only willing to try it since I was basically in labor, just needed the contractions more consistent. It gave me horrible diarrhea for a few hours, but it did work and I had my son that night. I also got dehydrated halfway through labor and needed fluids through an IV. I don't recommend it and plus it doesn't always work unless your body is ready anyway. I would never use it again because it made me feel miserable and I hardly had any energy for pushing.
This is incredibly dangerous for you and your baby. A pregnant women should NEVER attempt self induction. The fact that the castor oil may cause you to vomit is the least of the complications. Baby is premature and castor oil can distress baby enough for him/her to pass muconium which can sometimes result in life threatening consequences.
I also do not suggest it. Pregnancy is 40 weeks, not 36. You also need to bear in mind if your body isn't in labour on it's own nothing will work. You only have a few weeks left. Let baby come when it's ready instead of forcing it to beforehand. I understand quite well how much you want him out (I had hypermeisis) but your baby will do much better letting your body naturally do what it knows to do.
I would NOT do that this early! the abby is PREMATURE at 36-37 weeks! IT is not full term and some abbies come out at 37 weeks even with problems! Babies need 40 weeks or as long as they want to stay in there, if it will send you into early labor then you should not even try to induce as being early it could go fast and anything can happen with the baby and be stressed from contractiosn being early!!!!!
I really don't know where u can buy it from, but I heard some stories from my friends who used it to induce labour, and all 3 of them said that it worked within an hour or two, so it works, however, you should check with ur doctor before taking it, especially that u r still in ur 36 week, if ur doctor doesn't support inducing labour, which I honestly agree with, try asking ur midwife if u have any.
Just make sure that u will not hurt ur baby