Why can't i find a jungle biome on mincraft?

I've searched by boat, foot, etc. I'm in survival and i need watermelon seeds, and cocoa beans. Any advice?

Try a different seed, Look here for some seeds.
http://www.minecraftseeds.info/

Without knowing your seed, there's no way for use to offer any advice other than to keep moving.

If you have cheats turned on, switch to creative and fly instead. Or just spawn some cocoa beans, jungle wood/saplings, and watermelon seeds.