Yeah the 'basic' sets I got in the 70's had plenty of wheels, slopes, windows, and those weird articulated arm people- the mythic age of children building everything out of rectangles never really existed.

The Lego Store near me has bins separated by color. You can buy as many pieces as you need of each size. Kind of like how you buy bulk candy or nuts at Whole Foods.

For the price they charge for that, though, they'd be better off buying one of the creative line boxes and throwing out all of the non-rectangular pieces. Which would be dumb to do, but apparently they want those pieces and none others.

It seems they have:

https://www.bricklink.com/v2/catalog/catalogitem.page?S=5576...

https://www.bricklink.com/v2/catalog/catalogitem.page?S=6177...