You can use a 3 wire 12si as a direct replacement for a 10si, and the stock version is available with output up to 94 amps. If you use all 3 wires it will put out full voltage at just a few hundred RPM above idle. They are also cheap and very easy to find in any auto parts store.
There are newer alternaors (like the CS130) that have higher output, but they are more expensive. Unless you need more than 94 amps, the 12si is a good choice for a V-belt system.