A flashing load is made by getting one of those old-fashioned "buttons", and inserting it in the socket under the bulb. They were once common for Xmas displays- and are still available. They are limited to 60 amp loads.
The problem with using several at once is that there is no way to have them trip in time with each other.
Still, the 1/2 amp fluctuation is useful in finding circuits.
I have also found the usual circuit toners to be useful in finding the appropriate neutral in the panel.
Adding a large load, as with a space heater, might also help find the right wire.
