Official Nike Clemson jerseys are only available this year in the number 16 (for the year 2016), however some number 3 and 4 jerseys might still be floating around from last year.
Aliexpress is another option, but the jerseys are knockoffs and don't always look too good. However Aliexpress only has Deshaun Watson, Sammy Watkins, and Tajh Boyd jerseys available.
Long story short, you won't find a "Renfrow" jersey unless its a generic number 13 Clemson jersey on eBay. You might wanna check there.