I read an essay by Ruth Reichl on hummus and importance of good tahini. The
brand I typically used (white metal can with a camel on it) was bitter and often tasted rancid but I never thought about it. Ruth's essay drove me to seek out other tahini. While I've only tried a couple, I'm quite happy with Cortas brand, which you can order online. My favorite Middle Eastern resto uses that brand as well.
As for making your own tahini, are you on Facebook? Paula Wolfert has a terrific Moroccan food group with some astonishingly great cooks (by Paula's standard). You might want to jump on there and ask about making your own tahini. My guess is you'll get a great response there.