It's been some time since I had one of these made. But thankfully, there are even more great suppliers and better prices than when I was doing this years ago!
Please note, I have not used either of these companies for stamps yet, but I found them with a quick google search. I will have one made and do a video when it arrives! FUN project!
http://www.overnightprints.com/rubberstamps- Overnightprints is a company I have used in the past for photo printing. Their customer service is good. This is for a large self-inking stamp for $14.05. Self-inking is good if you only want to stamp in black for like a return address.
http://www.rubberstampchamp.com/custom.aspx?id=30 Rubberstampchamp.com allows you to make a custom rubber stamp with a handle in a huge range of sizes. They even have round sizes! And they customize with your artwork at no extra charge. Their prices are great - averaging around $15. They also offer free shipping on orders over $10.
You would prepare your artwork like I demonstrated in the "Preparing your calligraphy for printing" tutorial. Then upload it to the site.
I hope that is helpful and if anyone has used a different vendor or has feedback on one of these, please let us know!