Battery for DIY Electric Surfboard

I am building a dual-motor electric surfboard with SSS 56114 360kv motors connected to 2 80mm 3d printed jet propulsion units. The ESCs I am using are rated for 90v 400a. All of the components are water-cooled to limit overheating. I have already purchased all parts except for the battery and the board.

I think I want at least an 18s battery (66v). Does anyone have any information on where I should buy a battery from? For anyone who built an electric surfboard before, what battery did you use?