"Best gun shows" would be pretty subjective depending on what you'd be after as well as the fact that gun shows have lost viability due to the Internet and endless panic seasons.
There are 3 promoters doing shows in the state:
South Carolina Arms Collectors Association (SCACA) - Puts on shows in Greenville (TD Center) and for this year at two venues in Columbia (Jamil Temple and SC State Fairgrounds). If you are looking for old parts these would probably be your best bet. This is supposedly the last year that they will be doing shows at the Jamil Temple. Non-firearm vendors are kept to a minimum.
Mike Kent Shows - Puts on shows in Florence (Civic Center), Myrtle Beach (Convention Center), and in Ladson (Exchange Park). Shows are a mix of gun dealers and flea market/ancillary items vendors selling stuff that have little or nothing to do with guns. You might find someone selling old parts here but chances are not as good as at a SCACA show.
Great American Promotions - Puts on very small shows throughought the state many in areas not near larger cities. I would not even bother as these shows are rinky-dink and the vendor prices are outrageous even by today's standards. Great American shows suck, period.
For schedules Gun Show Trader is your best bet online:
https://gunshowtrader.com/