There is a great place online where you can get your cauldron and many other Halloween ideas. Go to www.halloween-online.com/...projects-witches-cauldron.html
You could actually find a miniature Cauldron right at your home. Just try to find a useable pot or a pointless one somewhere in your kitchen. Even though it won't be as big as movies depict, it can still be like a makeshift Cauldron.
You can usually buy them at places that sell Halloween decorations and Halloween party decorations and party favours at around halloween. I have a purple topped one with a spider on it that I got at Walmart.
A great place to buy decorations is at a Party Tree or Party City. From experience, when Halloween rolls around, everyone gets the best decorations from Party Tree and Party City.
Try party city!
Party City
Party City has great Halloween decorations at a killer price, also you can go to you nearest Halloween store and buy some as well. You do not have to buy them online.
For great and spooky Halloween decorations, your best bet would be go to a store specializing in party decorations, such as the store Party City and Halloween Express.
There are many places to buy bat costumes for Halloween. People can purchase bat costumes at Party City. Party City has a wide assortment of costumes.
you can probably buy one at party city or a Halloween shop
You can purchase Halloween goody bags in Party City or Target, or buy them in bulk from sites like Amazon.com or here (http://www.mypapershop.com/halloween-cello-bags.html).
Preferably a shop - although there isn't any particular one. Anything to put a range of different sweets into a kid's cauldron or pumpkin.
You can buy Halloween wrapping paper online from Halloween USA, Party City, Amazon or Ebay, or here at Ghoul Gallery: http://www.ghoulgallery.com/Ghouls/Page_Gift_giving.htm