A headshop/tobacconist.

However, some countries have banned the selling of paraphernalia so you may need to buy one, illegally, from online.

Alternatively, in the US, I believe bongs can be bought legally online.

Hi, I am pretty sure that you can purchase any bongs on that cool us head shops online https://likebongs.com/ . Recently I have ordered some cheap bongs and should say I am pretty satisfied both with my choice and prices. Hope that info will make sense for you. Cheers