This may not be as specific an answer as you would like, but while currently building a home to the EPA Indoor airPLUS construction specifications I discovered that although we have made great strides with paints, we have not come as far with stains and sealers.
I recommend you try the Greenguard website. This site deals with stains and varnishes, but will lead you to manufacturers who are excelling in this area and probably can meet your specific need.
These brands are a little off the mainstream path, so you may not have heard of them, but web locators will hook you up with local experts.
For more information:
Architect Matthew Bremer recommends Laticrete grout and caulk in his Q&A "We're remodeling our bathroom due to faulty construction. Can you offer some green pointers?"
And check GreenHomeGuide's "Making Your Bathroom Healthy, Efficient, and Comfortable" for green bathroomdesign, construction, and maintenance advice.