I take it you are not being serious! - these tubes went out of main production over 20 years ago. They are now only made in small batches by specialised companies - hence the limited stock levels. just like tyres for my Morris Minor, their tyres used to be 10 a penny, (or more factually correct, one for £21) now out of production, they are very costly. Same with these Goodyear 8.00x4's once plentiful, now difficult to find.
Someone must have a few on a shelf somewhere????
FB