While it doesnt meet your description perfectly, RaR (Rise and Rule) is a good senerio with modern units. It is a variant of Double your Pleasure for Civ 3. This one has more units for all eras, not just modern. However the number of units in the modern era has expanded termendously.
It actually allows, infact requires, diversified armies. If you want to just build tanks you are in a surprise. Tanks are limited due to the terrain limitations imposed in the game.