Need help identifying single bolt toilet mount design

[sippyyy]

Need help identifying single bolt toilet mount design. Copper overflow tube gave out and need to replace, but this toilet does not have the traditional two bolt mounting design. A single bolt connects the bowl to the tank by threading into the overflow/flapper assembly. I'm guessing I need to replace that entire copper assembly, but I'm not having much luck finding anything. Photo links provided below, TIA

https://1drv.ms/u/s!AmxDALIplKx6gnJJSPc6RtxDldWa

https://1drv.ms/u/s!AmxDALIplKx6gnPxfhXnz5Qm6fAw

 

[Geofd]

I haven't run across that style before have you check with the manufacturer the name would be behind the seat and style# would be located in the tank pressed into the china or stamped in black

 

[RenewDave]

I think it’s new toilet time. Good luck finding parts. I’d like to know what brand that is. When all else fails, check with Kohler.