Finding a publisher is very difficult unless you have established a name, as in most cases the publisher needs some assurance towards reaching sufficient sales levels to provide a good return for their investment.

You could always self publish and market yourself via companies like Blurb, (Print on Demand companies to minimise outlay and storage problems) etc., but as most will tell you, success in high sales requires total commitment and a lot of foot work plugging yourself.

With 5000 photo's I would try and consider a theme, so that your subsequent book falls into the genre categories that may sell.

Also checkout and read up on the mountains to climb that ordinary writers of novels etc., face; as the marketplace is much the same, if not harder, when you consider photographic books cost a lot more to produce.

Best of luck