While there is the fabric you can buy (rather expensive) you can use any fabric you want, really even printed. You just iron on a piece of freezer paper and cut it to 8.5x11 and run it through your printer. I typically use white Kona cotton. However, you want to make sure that the printer you use has the right kind of ink, I'm out of practice on knowing exactly which printers are better. I know my black and white laser printer prints great labels that do not run, smear or fade.
I need to do a bit of photo shopping to combine a picture I took of my friend's face that I am going to put on a free clip art image of Supergirl. My friend just retired from teaching and I am making an alphabet quilt in her honor (she mostly taught English). It's very simple, just 8" blocks of fabric representing each letter so A is for Apple, B is for Bear, etc. Her name is Suzan and so S is for Super Suz
One of the ladies in my small group has a color printer and will print it for me and then the top is all cut and ready to go together.
For others that may be interested in the idea, having spacer blocks at the beginning and ending of the ABC and XYZ rows make the quilt 5x6 blocks. Add a border or two and you have a nice crib/lap sized project. I quilt the letter into each block and then do a meander or other simple quilting in the border.