Just buy however many 1% resistors as you need to put in parallell to get that. I would guess 47 4R7 1% 0.3W metal film resistors, all soldered to a simple flat PCB with a slot either ground or etched into the middle, to make a simple 2 wire ( or 4 wire if you want, but for a PAT with a 2 wire measurement pretty moot anyway) 0R1 1% resistor. You need a lot of resistor, simply because the test current will be around 6-25A AC, and that is a lot of power for a metal film resistor to handle, so a lot of resistors is needed. Will be marginal with 47 resistors, they will be horribly overrun, but as the test is normally short duration they will survive short term, though for longer testing 100 10R 1% 0.6W metal film resistors on the big copper heat spreader will survive, you will just need a big soldering iron to solder all of them on, or get solder paste and a lot of 100 1206 SMD resistors instead on the boards and reflow it instead.