Thank you very much for giving us the opportunity to consider your novel, which we have looked at (but not read) with interest. However, I regret that we (don’t just blame me!) have reluctantly come to the conclusion (I regret the reluctance, not the conclusion) that we could not publish it with commercial success (could not exploit you enough financially, or laugh much more than we have already).
At the risk of telling you (or wetting my pants if I tell you) what you know already, may I respectfully suggest the following:
Double check in a large bookshop, or on Amazon or in the twice-yearly ‘Buyer’s Guide’ of the Bookseller magazine (or in your own navel), precisely who are the publishers now of your fiction category/genre.
Call the publishers to obtain the name of the relevant editor; it is rarely productive to speak to (or to try to speak to, or to have predatory sex with) her/him in person.
Then send to each editor an alluring 200-word blurb (as on book jackets; don’t give away the ending!) (Why would editors need the ending?), the first chapter, plus perhaps two others, and an SAE (Sorry, All Excrement). The covering letter should state as precisely as you can the category/genre of the fiction you are submitting – cite successful authors in your genre, especially those published by the particular imprint you are contacting (because publishers won’t understand which genre it is, don’t know which authors are successful in it, and forget who their own authors are). Again, a helpful bookshop (one with the time to help because people are buying e-books instead) may be able to advise you.
Remember that acquiring a literary agent is even harder than finding a publisher (you have to find a publisher first, and finding a publisher is impossible). Owing to pressure of submissions, I regret we cannot reply individually or provide constructive criticism (or destructive criticism). (A writers’ group/writing course may help with the latter.) May I wish you every success in placing your work elsewhere (not disturbing us again and not stealing our profits by self-publishing an e-book).