A wonderful company that will do custom letters is The Bee Charmer. Their website is
www.beecharmercards.com and they do a FABULOUS job on their letter shirts. I have ordered 2 from them and they are very well made. I plan on having them make a custom fabric letter sweatshirt in a couple of weeks. Just drop them an email and they wll provide the mailing address to send the fabric...I was quite impressed with their service!