im not particularly known for slapping, though i use it frequently. i am friends or at least acquainted with some of the great slappers: jeff from BR549, kevin smith, mike bub, mark rubin, jack hanlon, jt huskey, etc. but the best of the best is dave roe, here in nashville. he is on the road with kathy mattea but he's usually found thursday, friday, and saturday evenings on lower broadway. he played bass with johnny cash for several years, dwight yoakam, stan martin, and don kelly and is acknowledged around this town to own that style. there may be someone better, but nashville doesnt know about him.
secondly, modern rockabilly is a different beast from old rockabilly. some things are more developed and mature with modern rockabilly. rockabilly that is true to the old styles is the exception rather than the rules. hair is bigger, amplification is more extreme, tattoos more prevalent, guitar playing is showier (and youd think everyone back then played gretsches exclusively), and bass is slapped much more and much better.
modern rockabilly is a distinctly different music now.