First question is how low a pressure (at the pop up) are we talking (you've got to start with static pressure and then account for pressure drops through backflow devices, pipe friction, valves, etc).

But regardless of the answer, the only thing that comes to mind would be possibly replacing the nozzles in the pop-ups with MP-Rotators. Other that redesigning the system or increasing the static pressure (i.e. pumps), these are the only thing I've ever heard of someone using to improve a low pressure situation.

Here is a link that might be useful: MPRotators (2000 series)

Sprinkler heads that operate at a lower pressure are subjective. Low pressure as compaired to what? There are no heads available to meet ALL low pressure conditions ( only so low they can go at the spacing you have installed at ). You need to know what nozzels you have installed now and if there are nozzels available for your heads with a lower flow rate. Your problem is flow and not pressure. If a nozzel change makes a SIGNIFICANT change in pressure required AT THE HEAD then your problem may be resolved without redesign.

However, you need to begin at the beginning. Your landscape irrigation is limited by the water source. I am
going to assume that you are on "city water"

At minimum you need to know the;
1] size of service line
2] size of the water meter
3] size of feed line ( from meter to house or from meter to irrigation main line )
4] static water pressure
5] size of irrigation mainline
6] total system pressure required for your sprinkler system

Is the sprinkler system connected off the water meter prior to entering the house? Or is the connection made at a hose bib where water has to go through the household plumbing? If the latter, re-connect prior to entering the house.

Your problem is the sprinkler system "asking" for more water then the piping can efficiently provide and the resulting pressure losses are to great ( assuming there are no leaks ). If the static water pressure is 40 or 50 psi, then a sprinkler system can be designed without the need of a booster pump ( yes even lower static presures can be designed around,if the water window is sufficient and there is no limit to the valve stations you wish to install ). There is not enough info here to know all of your options, but "getting the system under control" may very well mean REDESIGN.

Note= Do not consider a booster pump unless the pipe sizing can provide the system flow demand. A pump cannot ( and does not ) "suck" water from the city main line. My business is booster pump systems.

boosterpumptech

The only Sprinkler I have ever found that works at low PSI was the Rain Bird Impact Sprinkler model P2-R which operates at pressures as low as 15 PSI.

Unfortunately all current searches for the P2-R Low Pressure Mini Bird are all showing "Out of stock"

I hope that the P2-R has not been discontinued. That would mean disaster for my pastures.