It has been my experience that the radiator passages act as filters for the debris, so that is the primary target. The usual flow through a radiator is rather generous, so most debris will be found there. Any that isn't found there has settled somewhere inconspicuous to the velocity of the normal flow. For instance, some particles at the bottom of the cylinder jackets will usually stay there indefinitely and your flushing activities have a low probability of exceeding the natural flow rate, but you're welcome to try.
In days of old, the, "pros" used a recirculating pump with some serious chemical content. One place where I worked had a huge vat where the radiators were boiled over night.
The next day, the leaks were soldered shut because the passages were a copper alloy and would accept lead solder. One ingredient would be oxalic acid. I would be fearful to inflict such corrosive contents on modern radiators. I would back flush the radiator and expect some particles to be carried out of the radiator simply due to mechanical forces.
Now that there is a mix of ferrous metals and aluminum exposed to the water flow, and computer aided design has accomplished removing all possible excess quality in the radiator fins, a proper flushing solution is no longer a cup of non-foaming detergent and a pound of oxalic acid. I guess somebody makes a proper flushing product, but I don't know what it would be. I would just rely on the water velocity for my first attempt. Only if the radiator refuses to surrender its load of particles and the engine is in danger would I try something more chemically active.
ps, Don't neglect the heater core(s). They need to be addressed separately in order to get a good velocity flush.