The DEAP library (a Python library for EAs) contains some benchmarks. In particular, you may want to look at the following functions
dtlz1, dtlz2, dtlz3, dtlz4, dtlz5, dtlz6, dtlz7
Besides the DEAP library repository, you might want to look at several well ...
(Disclaimer: although I have never seen a formal definition of unknown search space, here is my attempt to define it based on my knowledge of search and search algorithms in machine learning and evolutionary algorithms; I am aware of a definition of unknown environment (see chapter 2, p. 44, of Norvig and Russell's AI book), but that definition is different ...