Rather than provide a list of Juggling retailers which we would have to keep up to date, we thought it would be better to point you in the direction of the IJDb vendors list as it's probably the most comprehensive list of Juggling retailers on the internet!
Shopping for a suitable hat is a tricky business. Wherever possible, it's best to buy hats in person as this gives you a chance to try them on. This is especially true for Nils Poll hats as their sizes are only approximate.
However, for a lot of people mail order is the only option, in which case talk to your supplier. Some juggling retailers are willing to allow you to send a hat back if it doesn't fit you and will exchange it for a replacement.
Most of the suppliers listed on the IJDb will be able to sell you a hat, so I suggest you pick one near you and give them a go!
When it comes to buying the books and videos mentioned in the resources section, you might have a little more trouble. A couple of the titles mentioned are out of print, and are a little hard to get hold of.
In which case, I would try asking your local juggling retailer first, and if they can't help have a look on www.amazon.com or www.ebay.com to see if you can track down a copy.