Remember that you can always write a query letter to closed houses. If they accept your query, then your manuscript becomes solicited. See my post on this here.
Here are some publishers accepting unsolicited manuscripts:
Knowonder (Chapter books mainly, some unpaid work)
Kane Miller (Educational)
Lee and Low (Multicultural)
Orca (Only for Canadians)
Annick Press (For Canadians)
Move Books (boy-centred middle-grade novels)
Melusine Muse Press (proceeds to chapter book challenge or a charity)
Your Kids’ Creations (an anthology for children to submit to)
Children’s Book Academy posted about this topic in July 2014.
However, this is only a start. Please do your research to make sure that the publisher is a correct fit before you submit.
Feel free to add on to this list. Also let me know of any changes.