One can buy embroidered shirts in various places online. Ebay and amazon are both online marketplaces where one might find used ones. Macys will allow you to order embroidered shirts on their website.
One may try embroidery shops, online stores and shops. One may also try Ralph Lauren's official Polo site, which would be the best option. One may take into consideration that he may want to purchase the shirt first then have it embroidered.
There are several places online where you can buy custom running shirts at a low price. CustomInk.com is a great place to start, they have low prices and you can make any design you can think of.
From your mother
The best place to get custom screen printed t-shirts is on the site Custom Ink. This site has an easy to use design template, quality shirts, a large selection of shirts and fantastic customer service for a great price.
If you want to buy screen printed t-shirts with custom design on them there are lots of sites online you can go to. Examples of these are Vistaprint and Spread Shirt.
There are numerous online retailers that allow you to create an original tee shirt. For example Custom Ink allows customers to design shirts online and gives free shipping on orders.
There are many online customizing companies that you can choose from. "Buy Corporate Apparel" is a professional company that provides customized corporate apparel, business casual shirts, customized t-shirts, etc.
You can buy them online (: