I am not a writer (yet!), but I have been working in the computer field for over 10 years and would love to put in some time volunteering my services as a subject matter expert (SME) for programming and computer related story components. Is there a central place that such SMEs can peddle their knowledge? Is anyone in need here?
For better or for worse, writers that need fact checking generally do their own research (or ask a friend). This may have to do with the fact that writers don't like "outsiders" meddling in the creative process.
But...people who have access to a unique cultural context or deep understanding in a specific area of knowledge often have compelling and insightful perspectives to volunteer.
Don't wait for others to come to you, find your literary voice and produce your narrative!
I seem to be repeating myself a lot, but I would recommend creating an account at CritiqueCircle. This is a web site where people volunteer to read each other's work and offer feedback and critiques on the story as well as the writing in general. Your expertise might be handy for some writers, and this would be a good place for you to let people know about it. You can also take advantage of the site to find other folks who can read your work and help you out as you develop your story. The site is free and they offer a number of handy tools to help writers.
I'll have to agree with the simple, "No," regarding the existence of a one-stop experts forum for consulting work, but depending on how well rounded your skills are across some specific disciplines there are a few very satisfying ways you might be able to volunteer your services. I'm only going to mention two here for the sake of brevity.
Become an alpha or beta reader for someone you respect. It can be both enjoyable and rewarding to be a reader for a good writer. The other way I have in mind might be outside the scope of what you have in mind, but if you want to become a writer yourself there are few better ways than to become a writer's personal assistant. It's probably not given as much attention as it should be, but many writers at the very top of the food chain use one or more research assistants. Obviously, this is a much harder situation to get yourself into, but much like young photographers who find a mentor and simply follow them around incessantly until they let you work for them, this or an equally persistent approach may be what it takes to get you that edge into the writing industry. It probably sound obnoxious, and it is, but sometimes a writer's got to do what a writer's got to do.