I need to find a psychiatrist who can help me cope with caring for my mentally ill manipulative 89 year old mother with brain cancer.

Your profile says that you're the "lone caregiver" for your mother, and that you're not only suffering from mental issues but physical ones as well because of that.
That in itself should tell you that something has to change NOW or you will be in the statistics of the caregiver dying before the one they're caring for. PLEASE don't let that happen! You are important in this equation as well.
Your mother needs to be placed in the appropriate facility, where she will receive the 24/7 care she needs and you can get back to just being her child.
Caregiving is the hardest job any of us will ever do and when you add someone that's mentally ill and manipulative on top of that, well that is really more than anyone should have to deal with on their own.
So please start the process today to get your mother placed and look into bringing hospice on board as well.
Then you can start the process of dealing with the damage that's been done with a good therapist or counselor.
I'm wishing you the very best in getting your life back on track and healing old wounds.

Since you want a psychiatrist for yourself to help you cope with the caring for your mother, maybe a therapist might be a better match, unless you are thinking you have a mental illness?

I'd ask my PCP for recommendations. Ask friends also.

Be prepared for it to take a few visits to establish the trust you must have with a psych doc.

And be prepared for the fact that your mother seems to be at her EOL. No amount of therapy can completely prepare you for the passing of your mom.

I was not on great terms with my mom when she died last year. My psych doc really helped me to come to terms with it and not feel guilty 'after the fact'.

If you are caring for mom now--you already have some issues, right? It's good you are not in denial about how tough this could be.

((Hugs))

Do you live with your mother ?

Does she require hands on caregiving ? If so are you providing that or does Mom have help coming ? How about meals etc , laundry cleaning ?
More info would help.

Perhaps it would be best for both of you if your mother was in a facility . You could visit and leave when needed .

Find one in your own area by looking online, our new yellow pages. Good luck. And do know that this is self-limiting. At some point, being both 89 and having brain cancer does limit ones ability to manipulate their world at all. Do consider care placement with Hospice when things become too much to handle in a home setting. Which I can only imagine happened yesterday.