Where can I get my mom a lift chair from donation?

Amanda4brian02, welcome to the forum. Before getting a lift chair, have your Mom try one out. She may really like it, or want no part of such a chair.

Gobon Craigs place. Facebook yardsale near you. Habitat for Humanity Stores. Thrift stores selling furniture.

Good question. I'm not aware of any places but if here in the US you can try calling 211 to see if they're aware of any places.
I purchased a nice lift chair for my late husband off of Amazon and it was at the time only about $700.
Make sure when you do get one that it has dual motors so you can adjust both the feet and the head separately.