As others have said, 05/06 was the last season. Before that, it was 93/94 with Mikael Renberg (38), Jason Arnott (33), Bryan Smolinski (31) and Alexei Yashin (30). Removing WHA players, the season with the most was 81/82 with 11 players.
Dale Hawerchuk (45)
Barry Pederson (44)
Neal Broten (38)
Paul MacLean (36)
Mike Bullard (36)
Marian Stastny (35)
Ron Flockhart (33)
Mark Pavelich (33)
Steve Bozek (33)
Bob Carpenter (32)
Chris Valentine (30)
The only seasons* with more than 3 rookie 30+ goal scorers are 80/81 (6), 81/82 (11), 83/84 (4), 92/93 (6), 93/94 (4) and 05/06 (4).
Only four rookies have scored 50+ goals in a rookie season: Selänne (76), Bossy (53), Ovechkin (52) and Nieuwendyk (51).
*Barring miscalculation.