I compiled a list of oil info about a year ago.
According to what I was able to find from spec sheets on the web, here's what is a 30 weight close to 12.0cSt at 100C (and not all are "synthetic"):
amsoil 10w30 = 11.9
amsoil 30w diesel = 11.5
Neo 10w30 = 11.75
schaeffer #702 monograde 30wt = 12.0
valvoline synpower racing formula 10w30 = 11.85
quaker state higher mileage 5w30 = 12.2
quaker state higher mileage 10w30 = 12.2
castrol syntec blend 10w30 = 11.5
castrol higher mileage 5w30 = 11.9
castrol higher mileage 10w30 = 12.0
anything higher is classified/marketed as a 40wt.
brands I had researched were redline, amsoil, royal purple, neo synthetic, mobil, scheaffer, valvoline, quaker state, pennzoil, and castrol.