I'm so sorry to hear about this. What a horrible experience with the sonographers too- the treatment of your healthcare team can make such a huge difference, especially in really difficult and traumatic circumstances.
I don't think it's likely or a good idea to try and bring it on in any way- if a substance could expedite a miscarriage, then whether it's natural or not doesn't really matter- every chemical starts somewhere, natural remedies can be harmful and I'd hate to imagine you took something which made it all that much worse.
It's such a hard decision, what to do after a miscarriage. A close friend recently decided to wait for it to happen naturally, pros and cons really.
Look after yourself x X X x x