Selectric Artists is open for submissions.  
Send a cover letter to query@selectricartists.com with your manuscript attached in .doc, .pdf. or .pages. Put the word "query" in the subject line.
​No phone queries. Ever.
Here's an ugly sentence: the number of submissions makes it impossible for detailed responses, so it's likely you'll only hear back if there's interest, usually within 2-4 weeks. If you receive another offer of representation, feel free to follow up.
Here's a do-as-I-say-not-as-I-do tip: a cover letter with a personal touch explaining why we'd be a good match is more likely to get me into your manuscript.