Piggly Wiggly @ Market Commons 1220 Moser Dr https://www.facebook.com/pages/Byrds-Beer-at-The-Pig/167739199945589
As @pimpinmidget said, the Piggly Wiggly is best bet. Green's on Kings Highway may have a different growler selection. Probably similar, but smaller bottle selection.
Check out the New South Brewing tour if you can. They only give them on Tues & Thurs and it lasts a little over an hour. Not a big space but definitely worth your time (It's free). You get 3-4 samples and it was packed with probably 50-60 people when we went last Summer. Agree Piggly Wiggly is the best spot for bottles. green's is pretty solid too. Here is a nice craft beer site for Myrtle Beach with various craft beer spots listed. Even has a tapfinder "On-Tap" so you know what's currently on tap for fills at some spots. http://www.myrtlebeachcraftbeer.com/findbeer/
For bars, Try the Grumpy Monk, it's a new place with around 50 taps, very cool place. Also atlas tap house great little bar with taos and lots of bottles
The Pig, but I bring my own stuff the only things local worth buying is One Claw it's better than their IPA, not much. Coast around. Atlas is a nice place , great bourbon selection as well as beer. MB prices on liquor and such are fierce.