If you do google search for DEPP flood insurance, you will find the link easily.
The premium is not too bad but one catch is that you will also have to insure one set of regulator, one BCD and one more item.
For me, I insure my Oly 5050 and Ikelite DS125 strobe under flood item and my Ikelite housing, dive com, reg, BC misc under non flood item for total of about $5000 and the premium was around $US150 a year. This way I am covered for theft, misc accident etc as well. Don't add your housing under flood item as it does not get damage when flooded anyway and it will only drive the premium up if you list it under flood item.
H2O is also available for US resident. I think you get it through DAN.