I was introduced to this fabulous resource today - my perfect pitch created by author Brian Grove, hosts an up-to-date list of approximately 1000 book publishers (worldwide) which are currently accepting submissions. They're all sorted out for you by their various genres, with handy-dandy links to the publishers submission guidelines page on their own website . . . a great site to bookmark for future reference.
Best of luck with your submissions!
I saw this video of Brian Selznick discussing The Invention of Hugo Cabret on School Library Journal.
The dummy book is a rough mock-up for a picture book, as visualised at this stage by the creator. They can be made for the creator's own purposes as part of the development process, but also as the final submission to a publisher.
Selznick shows us a glimpse of what an illustrated dummy for a picture book can look like, though normally you would create a full-size (or the size you envision it) 32-page* version for submission. There are different methods and styles of putting them together, but generally the idea is to have a rough model of the final book, to let the reader get a better sense of the flow and rhythm of the story and pictures, and helps them visualise it as a final product.
Even at the submission stage it is acceptable to have your dummy consisting of black and white sketches, though if your illustration work is unknown to the publisher you may wish to include two or three more polished colour samples to give them an idea of your style (always copies, never send originals). Don't do the whole book as finished art. It's not necessary, and chances are there would be tweaks and layout changes and you would be redoing them anyway.
Here is a more detailed explanation of creating a picture book dummy (ironically it's difficult to track down a good how-to with clear pictures). For the record, my first submission (for Fly, Little Bird ) was created from scratch, folding 16 sheets of A3 paper in half to create a 32-page A4 sized book, and hand stitched the spine together with wool. I scanned my original sketches, and created the layouts with text in Indesign, then printed them out. I used spray adhesive to adhere the printouts to my blank book, creating a very sticky and toxic-smelling dummy.
Hey, it worked! But even so, never again . . . I found that as careful as I was, there was still enough overspray and gluey fingerprints to make the pages stick together a little, which is distracting as you're trying to read it— I feel it messes up the pacing of the story as the reader stops to fiddle with stuck pages, or even worse, skips a page altogether (however, now you can get adhesive printer paper, which I'm sure would be much easier, cleaner, and less smelly).
So I now use "Option A", (as described in the article link above ↑): a binder from the office supply store, which has plastic sleeves and a clear cover opening where I can slip in a coverpage. I like the binders with a slim welded join, rather than a spiral bound one, so your double page spread can sit cleanly without a distracting spring running down the centre. To clarify:
I'm not necessarily saying this as a recommendation, just that it works for me. It's clean, the pages turn easily, and you still get the physical feel of holding and reading the book, and turning pages at the breaks. I also particularly like the ease that you can make adjustments to the dummy, by simply sending new A4 printouts with edited text or adjusted sketches as required — the editor can just slip the new page in and have an updated dummy! Too easy!
I did that for my Ruby Makes a Friend submission, as I felt the story and layouts needed a landscape (horizonal) format so it didn't fit properly in a standard binder. It worked well, too.
Print stores may also have suitable binding options for you, but you really don't need to spend a lot of money on a fancy binder or binding. It won't impress the publisher any more or less. It still comes down to what's within the pages.
Best of luck with your submission!
*32-pages is the standard length for a picture book, though there are also other less commonly used lengths. I believe it safest to stick to the standard when writing and submitting. Sophie's Big Bed was 24-page, but that was to fit a particular series of books for the very young. Anything longer than 32 pages starts to become an expensive endeavour for the publisher, so unless you are a sure-fire best-seller, a longer length may work against you.