Here is a working 100watt HPS ballast. Found in an OV-15 somewhere in Ontario, Canada. Every label is gone. I can tell that's it's likely a CWA ballast but need the capacitor value..what's the micro farads most likely for a 100w CWA HPS ballast?

Advance makes a CWA unit that uses a 35 uF cap. That's all I could find, since it appears most 100W HPS ballasts are HX.

If the ballast indeed works, you could use a multimeter that reads capacitance to measure it. Otherwise, if you like experimenting, you could use a multimeter that reads AC current to measure the lamp current, then, using a dummy lamp you don't care about like a 34 watt F40T12, substitute known capacitors until you find one that yields the correct current.

This is probably a Magnetek or a Universal ballast I think,  since it uses the spade connectors/terminals.