Saw this on Planet Catfish might explain why its harder to find one.
Considered ''Vulnerable'' to extinction due to overfishing by commercial fisheries. Average adult size captured by commercial fisheries has declined in recent years and now averages under one meter. In Puerto Carreno, on the Rio Orinoco, 5.5 tons of S. planiceps were harvested in 2001. Under Colombian law, specimens under 95 cm may not be retained. This would also make the small specimens imported for the aquarium trade illegal. Sadly, this law is rarely enforced.