Does it have to be aftermarket? Miller makes or made several pulsers for TIG & MIG. What machine & process?
I have an old Miller/Airco unit that will work on the 320-360 A/BP, Dialarc HF machines and any others that use a 150 watt 15 ohm rheostat. It is an Airco brand. I did see one like it on eBay once.