The local sporting goods store. Look for them in your area. They are the best because they will give schools discounts since they are buying in bulk, and will give you a discount since you are buying for a school as well. You should be able to look for them in the phone book.
A sporting goods store like sports authority may have them You may also want to look into eBay, Amazon or search other online wholesale stores, so that you can get them in bulk, which may be a cheaper alternative than buying at a local department store or sporting goods store.
Practice jerseys come off the same manufacturing line as game day uniforms; they are the same materials but simply have not had the numbers and lettering added yet. Most online and brick and mortar stores that sell uniforms will also have blank jerseys available in any wanted quantity.
Any sporting-good store which specialized in sporting equipment, and apparel should be more than capable of accommodating you with simple blank football jerseys.
Many local sporting goods stores will carry blank football jerseys. You can also try on-line as there are literally hundreds of suppliers of jerseys that can supply your team. Nike, Spawlding and other are brand names to look for.
Almost any sporting goods outlet store will have football jerseys that are blank. You can try looking up Reebok and check out their clothing options. Also look up and find some sports uniform supply stores, finding football equipment is very easy to do.
You can find blank football jerseys at many places, i would suggest big 5 as one of the top places to get jerseys. You could also get one on an online jersey site.
I would first try your local sports store. You can easily check online to see if they offer bulk orders. A discount is likely depending on how many you order.
At you can find a variety of blank football jerseys. They vary in color and font for numbers or name if you so desire. Also, you can mix and match between solid and two-color schemes.