About 5 years ago, when I had to replace a few, I got plain white ones from Home Depot. They were about $20 for 20 shingles. I don't know if they sell them any more or if they come in any other color. 2 years ago, I installed vinyl. ANYTHING is better than the asbestos cement shingles.
If you want to go that route, be sure to post up - I have lots of info to get you through all that.