There do seem to be many options in Ebay. I've tried two lengths:

These 10 inch long ones which I prefer, they sit just under the frame bar and are easy to find: https://www.ebay.com/itm/333171727979
These 7 or 8 inch ones, which I found were still too low and difficult to find: https://www.ebay.com/itm/293638099995

Both work great. You simply snip off the electrical cable, and flatten out the metal bar.

To refine the installation further, the spacer cylinder on the bolt that the Morgan ones need can be removed, and you can bolt them in with a shorter bolt. This reduces a pressure point on the seat base, and should reduce damage to the leather.

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2020 M3W