I've bought quite a few alloy cartridge units via aliexpress.
They were cheaper than anything I found on that auction site.
All were good enough that I put them on bikes I ride.
There were a few different varieties, lots of which I did not like the look.
I found some nice rounded ones listed as being for a scooter, they're on the Claud Butler (2nd pic).
More common is the type on the Dynamax Concorde/Moto GR.

You have to check the listings and make sure you have the right diameters and stack, and wait a while for them to arrive.