I feel your pain. Sounds like it should be a simple matter! When living in London (UK) I used to go frequently to Falkiner’s on Southampton Row. The whole shop is based on touching various papers! They have a pretty crazy collection though much of it would kill a printer. My printer proved able to survive anything I threw at it. Not without some coaxing though. I’ve probably spend a man age fishing shreds from the guts of the printer.
Have you considered paper for plotters (large format printers) usually comes in rolls as well as sheets. May need to cut down though. 280gsm might be a bit hard to get flat.