Replace broken 79M12 and 7805 voltage regulators?
You can replace them with any equivalent regulator, so long as it is better in terms of current rating and in the same package. 

For example, don't replace a 79M12 with a 79L12, because the M indicates a MEDIUM current level and is about 500mA-1A, while the L indicates a LOW current level which is usually ~100mA.

You could replace the 7805 with 7805 in a TO-220 package. The 79M12 could be replaced by any 7912 rated for ~1A.

Back in the day when that computer was produced, it was more expensive to produce a regulator which could do 1A vs. one which could do 500mA. It's still the same, but as manufacturing methods have improved, the price gap has shrunk.