Sorry, you won't find mechanical variable capacitors that large. They would be physically very large and impractical.
The best I can think of is an op amp capacitance multiplier circuit in conjunction with available standard variable capacitors, but realize such circuits have the steep limitation that one end of the capacitor is connected to the power supply ground. They also have a steep limitation on how high a frequency they operate at. 10KHz and above gets iffy. They also exhibit larger series resistance and leakage current than physical capacitors.
The usual route is to use a switched capacitor bank similar to a resistor decade box. Depending on the application, you might be able to use electronic switches.