If you haven’t noticed, Solaris 10 is not available for free anymore. At least the patches. It’s Oracle after all.
Security patches were originally available for free when Sun stil exists but not anymore now. From PCA site:
Unlike before, even security patches are not available for free anymore.
So you’re screwed if you don’t have one. You’re better off installing OpenIndiana instead.
In case you’re one of the lucky folks (like me /hahahaha) having office Oracle account with Solaris support contract, I suggest checking out PCA to ease up installing patches. Also make sure to install it through OpenCSW for easiest update method.