We're mages, and we're resourceful. They may have Servants, but their Armored Truck was designed to be able to kill them, since it also was shooting at Maria. Therefore, it should also be effective against other Servants. That's our ambush tactic. Maria will hopefully wake up soon, but we should get the armoured truck into working order so that we can fight back. The most important bit is the wind cannon that the grunts were using on Maria. If the robot is gigantic, that just makes it a big target. Javier will use his flames, and if he activates his Fire Elemental powers, the mages can shoot Rider's mech with a literal fucking flaming tornado!
With the tank active, we won't need to worry about Nazi scouts because we can just rip them to pieces by turning the street into a Hurricane of Doom™. But not the Flaming Hurricane of Doom™. We need to save that to throw Rider off balance.
If Sakura filters her Hollow Element through the wind cannon, that might be even more effective than Javier's fire. Even if it's a machine, it's still a Noble Phantasm; a spiritual construct, so it should be effective, and the winds might be able to amplify the impact of the attack. IMPORTANT: Sakura's not at full strength, she'll probably only have one shot at this, so we should save it until we know where Rider is operating the mech from.
As for Maria, we'll have to hope she wakes up soon, because without her, we're in trouble, and Saver has made it exceptionally clear that it's petty, and thinks it's manipulative. Maria is likely to have lost some of her powers if anything when she wakes up, so that'll be trouble, but she should still be able to attack Rider with her sword beams.