I am not a huge fan of the Power poles, for the same reasons you suggest, no decent panel mount option and only available in two conductor. They also aren't weather resistant in any way and don't have any strain relief on the conductors. That said, better connectors aren't so easy to get. There are a bunch of circular/military connectors that will fit the bill, either from known manufacturers like ITT/Cannon or unbranded ones from Amazon.
If you want 3 conductors, you could also consider an AC power style connector like Smart Plug, just clearly label it!
If you want 3 conductors, you could also consider an AC power style connector like Smart Plug, just clearly label it!