I suspect that a factory making the drills would have had an installation jig to both insert and remove springs.
Getting the spring out - or in - can be hazardous - it's best to hold a large pad of cloth, or a flat plate over it while probing with a screwdriver. As the spring comes free it might well try to fly out as it uncoils - the cloth or plate should save you from damage. It's sometimes the case that the cross shaft with the gear that engages the rack can be knocked out from the spring end first - but do be careful in case there are retaining pins into a groove cut into the shaft - or some sort of circular retainer that needs removing. With the shaft knocked out of engagement with the spring, getting the latter out should be easier
Getting a coil spring back in can be entertaining.
One way that I've had success with is to wind the spring up very tightly and then tie it radially in four paces with a thin string. Then, as a compact unit, it can be slid into the housing, a flat plate of some sort held over it to stop if coming out as the strings are cut. Most new springs are would around their circumference with a length of wire and, if the spring is wound tightly enough, it might drop into the housing and the wire worked off. Again, be sure to use a plate over the spring the stop if flying out as the wire is taken off.
If the spring is held inside a detachable cover, the same process outlined about can be used.
If the either end of the spring is broken it can be annealed and bent to shape or drilled or formed into a circle to match up with the particular fittings used.
Two high-quality UK-made springs can be found here