A hydrostatic test pump might get you there, pressure wise. As Big suggests, it would take a bit of elbow grease to achieve 1 gpm with one. Realize that 1 gpm at 50 psig is about 23 Watts of power with no accounting for pump efficiency; typical human arms are good for about 100 Watts for a minute, and much less on a continuous basis. Leg power is better at some 750 watts continuous power. Maybe a gear pump and a bicycle frame...