MSC is a good source because they have ANYTHING you may want in the cutting tool area, but they are WAY over priced. McMaster has cutters too and while prices a little on the high side, they're still better than MSC.
I don't use anything but carbide end mills in my machine. I have found a source for a carbide end mill that's made in Korea that with one exception is the best end mill I have ever found for machining aluminum. I found it by accident. I had bought some end mills from Monster End Mills that are supposed to be American made, but they were the biggest piece of junk I have ever used. They are American made end mills, but they make them with Chinese carbide
If anyone is interested, shoot me a PM and I'll tell you what it is.