Ok - the smallest species of shark - presently available - is the Marbled Catshark (Atelomycterus macleayi) - grows up to 24" (61 cm) long. Smaller cousin of the Coral cat. Needs a tank of at least 170-225 gallons (6'L x 2.5'W x 1.5-2'T) - also a 300 gallon pond would work for a single adult for life. Priced at about $100-$200.
Next - is the Coral Catshark (Atelomycterus marmoratus) - Grows to 28"(71 cm). Tends to be more active and aggressive than the Marbled, and swim more than the Bamboos. Needs a tank of about 235-315 gallons (7'L x 3'W x 1.5-2'T)for a single adult for life. A 8'L x 4'W tank or pond could keep a pair of adult coral cats for life. Priced at about $90-150 each.
3rd the Gray Bamboo (Chiloscyllium griseum) - grows to 30". Needs a tank that's at least 360gallons (8'L x 3'W x 2'T). Priced at about $150 each.
The White-spotted Bamboo, Brown banded Bamboo, California Horn & Epaulette all require tanks or ponds of at least 480 gallons for a single adult.