I bought mine at an industrial place but you can order it online, I'm sure. I think I paid 'bout 11 or 15 bucks for a tube. I saw yesterday I have a tube in the shop of black partially used. IIRC I used it installing the acrylic in my companionway hatch but dang old age'ish, I can't remember....wait, two synapses rubbed together and a weak spark was generated, I bought it online...but can't recall the site. Ooh, ooh, I actually think it was Amazon.