Many of us have had experience with Yellow Letters and many of us go to Christy King for our yellow letters (and lots of other supplies, too). We would recommend Christy for the big lists for absentee owners, etc. But when you want to send just a few yellow letters of your own from doing your own prospecting you probably could use an easy way to put together a mass mailing (small quantity).
Here are a few links to the supplies you need and can easily buy at amazon.com as well as an MSWord letter template, an envelope template, and a spreadsheet formatted for a “mail merge”. Check out this website to learn how to do a mail merge or just go to the help screen in MSWord to learn and save yourself tons of time. You could even get your own font in your own handwriting at http://www.yourfonts.com/ if you want!!
We hope this helps and makes like a little easier for you.
John and Scot