Normally you can just make one up. BUT Atmel are quite difficult to get samples from. I tried ordering samples for a company I was working for a few years ago (It was for a legitamate product we were looking for alternative controllers for an existing product to broaden the range of devices used). After a month of not hearing back, I emailed them and got to speak with an field sales manager. After explaining what we were doing, what we were interested in etc.. he said he'd look into it. After another 3 weeks of not hearing from them, we gave up and used an Analog Devices ARM7 instead....
Microchip are usually quite easy to get samples from, you just have to have a non generic email address, remember if you make anything at hobby level using free samples then its only fair and good manners to mention the companies that helped you out either when writing it up or maybe a small advertisement or something.