Investigators said children aged between six months and 14 years were sold in illegal adoptions to couples from Europe, America and Asia for between $12,000 and $23,000 and taken out of the country.
While India has an estimated 30 million orphans, legal adoption is rare because of strict rules governing the practice and there is a thriving illicit market.
Police arrested two Darjeeling child protection officials, Mrinal Ghosh and Debasish Chanda, on Friday "for their links with the adoption scandal", Nishat Parvej of the state's Criminal Investigation Department told AFP.
He said three more government officials had "absconded", as the widening inquiry into the adoption racket embroils political and administrative figures.
So far six people have been nabbed over the scandal, including Juhi Choudhury, a senior member of Prime Minister Narendra Modi's party in West Bengal.
The head of the adoption centre at the heart of the scandal, Chandana Chakraborty, told investigators that Choudhury had been involved in child trafficking for several years.
Police arrested Chakraborty, a retired school principal, and her deputy Sonali Mondal last month after a tip-off from the federal adoption agency.
The pair ran the Bimala Sishu Griha centre where children were sold abroad through forged documents to couples for as much as 1.5 million rupees ($23,000).
Investigators said the scam had lasted for several years before they started monitoring the charity in June when federal authorities found discrepancies in their records and relocated all the children from the centre.
Chakraborty allegedly ran health camps to identify poor and unmarried pregnant women and persuaded them to give up their babies for adoption after paying them.
Experts say lengthy bureaucratic delays and complex rules in the adoption process push desperate couples toward the illegal adoption market.
Only 3,678 children were legally adopted by couples in India between April 2015 and March 2016, according to official data.
The latest scandal comes roughly four months after police arrested 18 people in the same state over a racket that saw gangs steal newborn babies from nursing homes with the intention of selling them.
