Garbage. No, really, you need to check rubbish bins daily, they often have a ton of useful technological components. Otherwise, check an inventor's or a junk dealer's shop, they have those in stock sometimes. Or, if you're a violent type, go to Tarant's docks at night and pick a fight with the local orcs, they use large pipes as weapons IIRC.

"...and that's a lead-pipe cinch!"

Sorry; couldn't resist.

You can buy large pipes from junk dealers too. Defending yourself against orc muggers is probably the best way to get one though.