I found few C19 -> Type F 3x2.5mm2 cable options.
They are a bit special and only mining operators use them.
For "regular" server guys, the 1.5mm2 cores are usually enough.

Zeusbtc:
https://www.zeusbtc.com/ASIC-Miner-Repair/Parts-Tools-Details.asp?ID=3550

Ultrabit:
https://www.ultrabit.nl/en/power-cable-c19-schuko-3x25-mm2-150-cm.html