The DWM1004C has entered mass production, it is definitely not obsolete ! I think it will be available with distributors very shortly.
Please note the mass production product is the module only, not the development board + module. So you may have to make a custom board to host the module.
Decawave is looking at the best way to provide a host board to customers but this is not ready yet.
The DWM1004-ES (engineering samples) that was a module + a dev_board will not be further stocked with distributors, and this is why deigikey marks it as obsolete. But the module itself will be stocked very shortly.