The reason for using an electric pump to supply vacuum for the brake booster in a fuel injected car is; the convenient source of engine generated vacuum also happens to be where the EFI's MAP sensor gets its signal from. Apparently, in some situations, the vacuum being supplied to the booster can interfere with the MAP sensor's readings. Many OEM's are using such electric vacuum pumps now, even with gasoline engines.
This is the pump I used: https://eveurope.eu/en/product...e2-vacuum-pump-used/ ;however, I couldn't find a current source of new ones. If I recall, it was just under $400. Companies like Hella and Bosch make similar units. Just buy one that's designed specifically for the application. Aftermarket EV parts suppliers all have them, as do Summit and Jeg's. Less expensive pumps simply run the entire time the engine is running whereas better ones have a vacuum switch that turns the pump on and off as needed.