I have MCTS and I was unsuccessful in finding any practice tests (like two years back). However, I followed the prep-guide on the MCP Website and came out unbruised on the other side. Of course, this can be expensive, but I am assuming your employer will cover you.
You have to know the APIs and base classes on almost all the MCTS-level exams. I don't know if this has changed or if the content has been updated for the Framework 3.5 or 4.0.
Good luck!