Hi Ladybird and welcome to writewords
Memoirs would be classed as non-fiction, so you need to search for agents and publishers that specialise in non-fiction - although, saying that, most large Agencies handle both fiction and non-fiction.
A good starting point is books/websites like Writers and Artists Yearbook (commonly referred to as WAAYB):
http://www.writersandartists.co.uk/
You could also check out published books similar to your own and make a note of who the publisher is and see if they have thanked an agent in their acknowledgements, then google the publishers and Agents websites and check out their submissions guidelines.
Good luck
- NaomiM