All large HVAC supply house's have pipe in stock in 26Ga.up to 14" diam. x 60" long. It is a common item, but if you pass though any combustible surface's it is a good idea to use the proper vent material with clearances recomended by the manufactuer.I got lucky we install many large boiler flues for mechanical contractors and was able to get twenty feet double wall positve pressure stainless steel pipe 14" id.