Looks like everyone is out of stock (Midway had some 24 Ga) however there is an alternative.
Rocky Mountain Cartridge make 20 Ga. in several lengths however they machine them from solid brass stock. These have thicker walls than the Mag Tech cases and use standard wads (Mag Tech recommends oversize wads). They normally make them for 209 primers and they also sell hand reloading kits
Main page
https://www.rockymountaincartridge.com/index.htm
Shotgun shells
https://www.rockymountaincartridge.com/index_htm_files/RMC Shot Shells & Load Kits.pdf
Reloading kit instructions
https://rockymountaincartridge.com/index_htm_files/RMC Load Kit Inst.pdf
Link to Circle Fly Wads
https://circlefly.com/
Circle fly wad sizing chart
https://img1.wsimg.com/blobby/go/d5...nloads/1c30n1443_939901.pdf?ver=1611285825376
Circle Fly brass shell reloading information
https://circlefly.com/bp-cartridges
The prices are ridicules, yes that are machined and would be great for retro use. Machining is impressive but cuts deeply in the beer funds.