Answered: Pneumatic Reservoirs

I was just wondering, are we allowed to use the FRC reservoirs in the VEX robotics competitions if we find a right fitting that goes directly on the black pneumatics tubes.

No, as per <R5>:

There is no special allowance for any additional type reservoir in rules, thus the only legal reservoir is the one included in the VEX Pneumatics Kit.

Ok. Then is there a way to buy extra reservoirs without buying the entire kit?
On the pneumatics page. There isn’t an options to buy more reservoirs

Currently there is no option for purchasing individual reservoirs.

Ok then this might sound stupid but are we allowed to repressurize the reservoirs during mid battle?

Although there is no rule against it, there is no configuration of legal VEX parts that would make this possible.