I have some spare 8-pin DIN connectors I never used. I could send you a couple if you need them but you can get a six pack of them shipped from china for $4. It would cost me as much to bubble mail them across the states...
The DIN connectors are solder lug type. You will need a multimeter or continuity tester to check which pins correspond to what colors. DO NOT TRUST color charts even for first party controllers due to variances in manufacture. After you've identified which pin goes to what color, you can cut the old plug off and solder in the leads to the new plug. Or alternately, you can buy a nice 8-foot DIN8 cable on eBay and cut off one of the plugs, then wire it into your control pad for a nice long cable that doesn't need extensions to play comfortably. Be aware that the Turbografx ports are all upside down on the console so any third party DIN8 cables will have the arrow key on the bottom instead of the top. Just make a mental note of that and you'll be fine.