MSC has a bunch .3120 reamers of different types including carbide if you have the $$. Enco has some as well and as usual they have better prices but a smaller selection. Enco is part of MSC from what I have been told. I buy a lot of my stuff at home from Enco because I am on a budget. Good stuff at decent prices compared to MSC or McMaster when it comes to machine tool stuff. Their selection isn't as good though.
www.mscdirect.com
www.use-enco.com