There are several companies recommend on the CC board
SPB Tours http://www.spb-tours.com/flash.html
People have recommended to use the Russian office of RO if you are going to book
Just be sure that who ever you use provides the "group Visa"
We have SPB booked for next year
Alexandr Pushkin, Carnival-Holiday, HAL-(old)Westerdam, Orient lines-Marco Polo, Royal Olympic-Olympic, NCL-Dream, Dawn-Princess, ACCL-Grande Caribe, Oceania-Insignia (3), Regatta(4) Marina (1) St Lawrence Cruise Lines-Canadian Empress
Scenic River cruise June 11,2012