You can search up "din 13 pin connector" on eBay or AliExpress and look for connectors.
It can be done for a few dollars with a soldering iron. Need a DIN 13 male and female connector, a RCA connector set, and a barrel connector pair.
(Heck, I have some free spares because AliE MOQ if you want to pay the shipping from NZ. Though, I think it would be cheaper to just buy them from AliE.)
If you are enterprising: there are a couple of vendors on Alibaba.com that will make a custom connector harness in bulk for about $5 that you can probably sell for US$50 a set.
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re: 12v power in the trunk. There is a brown connector in the front left on the trunk that just needs a fuse in the engine compartment to be energized. You can use a generic male spade adapter to patch in. Or you can buy the appropriate Sumitomo HD 250 male from Cycleterminal.com to connect in. Or many 90's-00's Honda's can be robbed of that connector from their main relay.
I don't remember which fuse, but it's the empty blade slot in the bottom right of the fuse box.