Maybe you are in luck. I was out in the shed looking for the 4’ brass starter loop of track and found a partial box of flex track, in Z!
660 mm long ea. in NS. My Amtrak train; engine and 6 cars could be a moving circle! But no you can’t have the train or power, but I will give you a section of track for the postage.
I still have your address from the caboose transaction.
I converted the steam loco to a Nn3 model of old RGS #20!
Edit; sweet talk me and I’ll solder it in a circle for ya, I’ll just put a stronger lens in my Optivisor.