Also, if you go to the Nasdaq website [1] there is a specific section on 'upcoming IPOs' and another called 'fillings', including SPACs.
Second, the major brokerage firms have dedicated sections for IPOs and allow 'qualified' customers to join the IPO price.
Lastly, you can filter the SEC Edgar database for companies who filed their IPO prospectus (S-1) [2].
[0]https://www.winston.com/images/content/1/4/v2/142711/SPACs-O... [1] https://www.nasdaq.com/market-activity/ipos [2] https://www.sec.gov/cgi-bin/browse-edgar?company=&CIK=&type=...