I've noticed many hits to my site recently with folks searching for 'tenebrae resources.' Last year, I posed the question on my blog - wondering if anyone had tenebrae liturgies besides those in the UM Book of Worship. I did receive some feedback, but the comments no longer appear to be available, so here's another post about tenebrae with some resources i've since found. (Please feel free to comment if you have more ideas!)
The most helpful site I've found so far is here, put together by Ken Collins. On his site, you will find information about what a tenebrae service is and how to conduct a tenebrae service, typically on Maundy Thursday, Good Friday, or perhaps Easter Eve.
Another good resource and complete liturgy can be found here, by Rev. Moira Laidlaw (who has many good liturgy resources that I check out regularly when planning worship.)
You can also find orders of worship/readings for tenebrae here, by Bass Mitchell, another site I frequently visit.
Hope this helps, and do share if you know of good resources.