Actually there's several species of sharks that are good private aquarists.
Here's the top 6 species
Coral Catsharks (Atelomycterus marmoratus) grows up to 28" long, requires at tank of at least 270 gallons (6'L x 3'W x 2'T).
Marbled Catshark (Atelomycterus macleayi) grow to 24" long, requires a tank of at least 225 gallons (6'L x 2.5'W x 2'T)
Brown Banded Bamboo (Chiloscyllium punctatum) or Banded Cat shark, grows to 41", and requires a tank/pond of at least 600 gallons (9' L x 4.5'W x 2'T).
White-spotted Bamboo (Chiloscyllium plagiosum) grows to 37", and requires a tank/pond of at least 480 gallons (8'L x 4'W x2'T).
Epaulette Shark (Hemiscyllium ocellatum) grows to 42" long, and requires a tank/pond of at least 600 gallons (9'L x 4.5'W x 2'T).
California Horn Shark (Heterodontus francisci) or Horn Shark usually grows to 38" , and requires a tank/pond of at least 600 gallons (9'L x 4.5'W x 2'T).
Note the tank requires are the minimums for a single adult shark of that species. Juveniles and pups may be able to be kept in smaller tanks. But if well taken care of they will even require a tank of size recommended or larger.
Also note that there are other suitable species that are available, just that these are the most commonly known.