MC-4 seem to be common. I buy a lot of stuff from China, cheap but it takes weeks. I bought some on ebay from exrell. A couple of days later I figured I better get some from a US source for a couple bucks more since I had company showing up and may need the extra panels. The ones from exrell in Singapore showed up about the same time as the ones from US. I ordered some more from Singapore and they also showed up a week later. I thought Singapore and China would be about the same shipping time but Singapore sure is fast. I have found that some brands of these connectors are hard to get apart. They even sell special tools to do it. I take my system down each year so ease is important. I smooth the locking tangs so they come apart easily. Wire is a tuffy. These connectors are set up for wire with extra thisk insulation which is hard to find. You might want to consider buying with wires attached.
