You're gonna have to hit the pavement a little to get what you want. There's a company that's nation-wide that sells Roofing & Siding material. It's Bass Supply and there may be one in your area. (Look in the Yellow Pages under Roofing.) If they don't carry it, you can try to talk to someone in the Home Center, like Home Depot or Lowe's, at the 'Building Materials Desk'. It may not be a stock item but since they deal with many roofing companies, you should be able to custom-order it. Add 10-15% for 'waste' to your actual square footage.
Certainteed sells a ceramic tile. It's cost is between that of real slate and imitation slate. You can call/write to Authentic Roof. They make an imitation slate roofing product. When you hit the pavement, be sure to ask for installation information too! You want to see if there's any special 'work' you need to do that won't void the warranty. And get a copy of that too for your reading!
Sorry, but this Forum doesn't handle Sales. My best to ya and hope this helps.