I can’t help you with locating a pump but I thought I would add some information which you might find useful. First, yes you do get pressure losses in water pipes due to friction loss. Different pipe materials etc vary but here are some examples for 500 feet of 3/4″ type K copper: 3.2psi loss @ 2.00gpm; 13.0psi loss @ 4.00gpm; 41.6psi loss @ 8.00gpm.
I think Robert was asking about the water tank elevation because he was thinking a larger supply pipe would be better than a pump. For a gravity system the elevation determines the maximum pressure available. Every 2.31 foot of elevation (head) equals one psi. If the tank was 100 ft higher than the main, you would have 43psi available there. If your house looks down on your neighbors, the elevation change would contribute to your inadequate water supply.
I would typically lean toward a larger pipe rather than a pump if that alone would be sufficient. But, It sounds like you have already talked to some plumbers, and I am guessing that you have a pretty good idea of what a new pipe would cost compared to a pump.
One more thing to consider is the flow velocity if you keep the 3/4″ pipe. As the velocity increase, erosion of the pipe increases and the effects of water hammer increases. Building codes, manufactures, etc. state different maximum velocities. 8(plastic)-10(metal) feet per second are typical maximums recommended for residential cold water. That is about 13-16 gpm for 3/4″ sch 40 pipe.
Hope this was useful