Pretty much any Lighting to USB cable will work. If you want it to last get something at least as thick as the one that came with the iPad. If you want to future proof it go for something a bit tougher, like one of the nice ones with the woven jacket and extra bend support at the connector. I believe there are even armored ones, if you're determined to give the cable eating rat a toothache.
Anyway, there are too many decent choices to go over here. Just don't grab the cheapest you see. Look for indication that it has Apple's Mi-Fi certification. If you are shopping on Amazon, include MiFi in the search to help filter out the crud. If you are shopping local at a known outlet like Staples, Walmart, or another store, pretty much everything will be certified.