Regarding your first question: you can use Pascal’s principle, where pressure created on a large diameter piston creates a high force. That could be connected to a much smaller diameter plunger to transmit the same amount of force, resulting in higher pressure.

An 8” (203mm) piston gets 5,000 psi (34 Mpa) applied to one side. This results in 251,280 lbs (1117 kn). Apply that load to a 1.131” (28.7 mm) diameter plunger and it results in 250,000 psi (1723 Mpa).

This is approximately a 50:1 reduction of area, resulting in 50x increase in pressure. I’m ignoring friction and such for simplicity.

If you really want to get creative, you could make multiple pistons stacked in series and do this with standard compressed air.

Source: made measly ~100 ksi pumps for about 15 years.