Pressure canning tomatoes without added acid
According to Putting Foods By, 25th ed. (1982), you can fill tomato jars with just hot boiled tomato juice rather than requiring additional acid, and then pressure-can them:


10lbs pressure / 40 minutes for skinned whole tomatoes
10lbs pressure / 15 minutes for sliced or diced tomatoes


... with some adjustments depending on jar size.

However, their extensive (11 large pages) section on tomatoes notes that whether or not acid should be added when pressure canning is controversial.