Google V8 release branches 3.7 and later fully support MIPS.
However, the MIPS development takes place here. The Google V8 bleeding_edge branch is sometimes broken for MIPS, as we port and upstream changes corresponding to their latest work. Sometimes it takes a few days for these commits to land. If you need the very latest build, you should probably get it here.
Here are some links to help you get started, this first set is general v8 background: