I see that you [link|http://www.britishdelights.com/drinks.htm|can]. That's just a brief Googling result. If you like it, I expect a more diligent search would reveal to you a less expensive supplier.
Also, consider [link|http://www.britshoppe.com/roborbarwat.html|this]. Much less gloopy than Sunny Delight. But do make it up somewhat weaker than the web page suggests. The suggested one part squash to four parts water would make me go crosseyed.