Feb 26 (Reuters) - Blank check firm Big Sky Growth Partners Inc on Friday filed for an initial public offering of up to $300 million on the Nasdaq, it said in a regulatory filing. The company is co-founded by Mark Vadon, former chairman of online pet products retailer Chewy Inc, who is currently the chief executive officer of Big Sky Growth. (Reporting by Ayanti Bera in Bengaluru; Editing by Shounak Dasgupta)