1500V DC rated wire (350MCM)

Howdy forum.

I am trying to find the right wire to go from a 1500V rated DC combiner panel to a disconnect. 
The only wire I can find in that high voltage is PV style wire with XLPE insulation. 
This style of high gauge PV wire's insulation is outdoor rated, but we are running our wire protected and inside conduit for its full run
so we could use something not outdoor rated. 
I can find some options in the Medium Voltage market, but it is very expensive.
It does not have to be 350MCM and could be AL or CU if we could find some size options.
Any vendors recommended or insights?
thx.

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