Where can I find a replacement green colored porcelain toilet?
I found this place on the net that has a lot of vintage plumbing. They had some green sinks and soap dishes and a pink toilet.

I didn't see a green toilet, but it looks like they do a lot of salvage work and their inventory changes frequently. Might be worthwhile to drop them an e-mail and have them notify you if one comes in.

Historic House Parts

Also, you could try online classified sites like e-bay. Here is an add for a turquoise/green toilet.

As to the thought of installing a monstrosity like that, may God have mercy on your soul. =)