I spent some time looking for air stones and gas dispersion tubes. The closest thing I found was the porous hose used for irrigation. The stuff I got is 1/2" ID and made from recycled plastic and rubber, and appears to be acid very resistant. I want to know what people use industrially.
For the lab you can get fritted glass on the end of a tube. But these are expensive.
Try phoning hydroponics stores because they may have bigger range and variety. Ceramic air stones are commonly available, which I have never tried myself. Other people to try are in the water + sewage treatment industry. They may able to help. Just ask for fine bubble air diffuser.