I haven't read it, but this book might be helpful to you: Trivium Mastery: The Intersection of Three Roads: How to Give Your Child an Authentic Classical Home Education. It doesn't look like it necessarily promotes the three stages idea.
Also, Charlotte Mason is a classical approach that doesn't use a strict Trivium division. The best online resources for CM are Ambleside Online and Simply Charlotte Mason.
There is also a 3R's classical approach a la Robinson Curriculum. Their website has lots of free articles and there is lots of information on their approach online. My homeschool blog has several posts if you're interested -- go to my main blog and it is in the sidebar (Kernels of Wheat).
I use ideas from Charlotte Mason and the Robinson Curriculum in my homeschool with great success, so if you have any questions let me know!