There are natural remedies and there are medicinal remedies; they don't cure so much as dry up the rash more quickly. There are homeopathic remedies, soaps, herbs (i know jewelweed lotion is used for poison ivy; not so sure about oak). I believe the medicinal approach is mostly steroidal cream to calm the itching. Lots of stuff out there, but all of it will take some time to work.
Check this link out. Hope it helps.
http://knoledge.org/oak/#remedies