Where to get counseling to deal with an abusive addicted sibling who has cut elder off from family?

If you're wanting counseling for yourself in dealing with anyone in your life with an addiction, I would start with Al-Anon as they help family members learn how to deal and cope with someone with addictions, whether it be alcohol or drugs.
Other than that you can "Google" addiction counselors in my area, as I'm sure there will be plenty that pop up, and there are many options available to meet online as well.
Best wishes.

Please give more info. Your profile says you r caring for MIL who lives 150 miles away and she is 94 years old.

I would start with Adult Protection Services and ask for a "well check". This will put the person on their radar.

I would contact the area on aging for the county where the elder lives.

Explain your situation and they can help guide you to resources.

Is the elder a vulnerable adult? Someone who has a diagnosis of cognitive/memory impairment, or is in poor health or physically frail? You can call APS to do a wellness check. You are already cut off from this person so any retribution from the sibling won't have any more impact. I'm assuming you don't mean the counseling is for the addicted sibling, correct? Or is it for your to cope with this dismaying situation? I wish you success in getting reconnected and peace in your heart for the things that you cannot control or change.

I think it’s going to depend how much power this person has over your loved one. Do they have POA? If so, then they have a lot of power, indeed. Then you need to get a lawyer.

If there is no POA, then you have every right to see your loved one if your loved one is open to it. If their mind has been poisoned, again, it’s a lawyer, because then you’ll want to seek guardianship.