If you have a Tap Plastic store anywhere near you they have all sizes of acrylic tube, rod, sheet, disks, rings, etc. Or you can buy from them online. Their prices are very reasonable.

Why are you running CO2 24 hours a day? If you turn it off when the lights are off the fish get a chance to rest from the high CO2, and the plants aren't using it then anyway. Even if you don't have a solenoid you could use the regulator pressure adjustment knob to turn it way down, then back up next morning. Don't use the bottle shutoff valve to do that because some cheap regulators, like the Milwaukee version, don't survive having the pressure turned on unless the regulator is adjusted to zero pressure first.