here's a site I found not too long ago http://www.basic.lanxess.com/bac/en/...r_information/
I'm not sure if it also has a metal deactivator or if it is needed at all in addition to their antioxidant/stabilizer but I'm on the same page as you when it comes to using antiox and metal deact in WVO or SVO I have it in my notes when it comes time to start making this stuff, however Biodiesel oxidation doesn't seem to be as big of an issue as in WVO or SVO but I will still use additives. If you have the time write to that company I sent you a link to and ask them about metal deactivation and see what they have to say, if you get anywhere write back and let me know, I dont think I've come across any other antioxidants that seem leggit.
As far as keeping your veg oil from oxidizing without additives one thing I know you can do is not to heat your entire tank of fuel apparently the heat plays a big role, in a cold climate use a winter biodiesel additive just to keep the fuel from not totally gelling up, most fuel pumps will push/pull the fuel even if it still has those little crystals in it but not if it's totally all gelled up, then you will still have to heat the fuel before the filter like in any good system. But also another important tip which I dont know too much about but have read is to 'loop your fuel return line'. This way the heated fuel doesn't get recycled back into your gas tank.