Yup…call your local welding supply house, they can hook you up with a tank lease. You might also think about using “Hy-Float” or a similar brand sealant. Florists and others with balloons use this liquid sealant in a std. latex balloon to keep them afloat longer, like days instead of hours. That is, if what you’re wanting to do with the balloons will mean longer is better. The Hy-Float or like products, can be purchased from most any floral wholesaler and I’ve even seen it offered at discount “party” stores that sell decorations and cards etc.