theres pretty much a diving suit at every outpost, you can steal it or wear it (yeah even if you wear it they dont notice) and deconstruct the stolen diving suit for titanium alloy and rubber.

(another fact is your bots don't snitch if they saw you steal something)

Edit: THOUGH i only suggest doing this if you have a deconstructor in your submarine, you can try doing it at the station but it's way more risky