(Bloomberg) --Flood insurance company Neptune Insurance Holdings Inc.'s shareholders are seeking to raise $368.4 million in a US initial public offering, adding to the flow of insurance firms debuting this year. The St. Petersburg, Florida-based company plans to market 18.4 million shares for$18 to $20 each, according to its filing Monday with the US Securities and Exchange Commission. Shareholders including co-founder Jim Albert, Bregal Sagemount Management and FTV Capital are set to sell stock, while Nep ...