If you have a hunt through the charity shops near you then you may find what you seek.
Specifically, some have large out of town retail units that sell furniture.
The Hospice near where I live has about six shops, each specialising in different goods, one of which is nothing but furniture of all types.
Have a drive around some of the office blocks on the Industrial Estates to see if any have Builders vans and skips outside signifying that there is refurbishment taking place, often old office furniture is skipped so you may also get lucky there.
Any Shops with Closing Down notices may accept a few quid for an office chair that they will soon not need.