I would buy them from the treasury department. I have not done this as we no longer purchse them but our daughter received several ans we purchased several along the years.
I do go to the treasury department site to keep up with the values, etc and trust that it is a good site. I belive some of the bonds my mom bought for daughter were through the site suggested below.
Our daughter received several as gifts when she was younger and we purchased a few ourselves. I completely agree that they are NOT a source for college funding. They are just a part of a very diversified portfolio we have for her but her main avenue for college funding is through a 529 plan which is fully funded at this point. Her bonds are all good and she has not decided where she will invest them as they fully mature.
I completely agree with others... if you do not understand exactly what you are investing in, don't do it.
We are very much into numbers, diversity and we do invest with bonds, numismatics as well as other investments which bring in much higher numbers for us. The bonds and numismatics are basically just something we hold on to and do not sell, reinvest, etc. Just make sure you know what you are doing so you don't lose money.