How much does maintenance cost for a typical car over its lifetime of say 15 years?

Maintenance here include scheduled and unscheduled, oil, tyres, etc.

I need at least two sources that give estimates for such a variable cost

I am rather confident that various classes of cars (and trucks/SUVs)
have sometimes vastly different maintenance costs. Do you have a few
specific vehicles you are looking at?

Consumer Reports often lists "cost of ownership" figures. These may
include fuel, insurance, and depreciation as well as maintenance.