EvBitz can make a custom length cable if you need it, using quality components. So can EcoHarmony (Viridian). Have purchased from both and they are both small reliable suppliers that are more than happy to take a phone call ( which counts for a lot).
This is helpful as I am going to be in the market for a longer cable quite soon.
Separate question about cable management. Don't fancy constantly trying to stuff a 10m cable into a storage bag.
Are there any cable reel solutions out there for longer cables? I wonder if the simple cable wheels that are used for caravan and campervans power cables would work OK? They are generally designed for 25m of 13amp cable, so I wonder if 10m of 32amp cable would work without damaging it?
Make sure you know whether you need single or 3-phase - the extra weight and cost of a 3-phase cable is a waste if your car can't use it.
For that size of cable, a garden hose reel might be more appropriate, though you may want to pad the centre out to maximise the bend radius.