I’ve never done it myself but met someone who does so all the time.

He starts by buying a hardback book. Looks up an address for the author. Then mails the book to the the author with a polite letter requesting an autograph. He includes the return postage so all the author has to do is sign it and send it back.

He has a house full of signed books. He said that authors by and large are very gracious and he has an almost 100% return rate.