FWT, a friend bought a Jensen from a local "donation lot" for $2500 (about 10 years ago). Interesting car, he found that most minor items were sourced from other British car. I recall most of the switches were Jaguar. A post below reminds me of being a kid, there was always a Facel Vega at the corner gas station/garage, needing some kind of service.
A Facel Vega sitting at a corner gas station.. now there's something you don't see every day.. well, except you did!
It is true what you mention about parts... raiding the parts bins of the bigger brands.
Many "smaller" car manufacturers - even established expensive brands like Maserati - didn't have the resources to design, develop and produce or commission their own accessories.
So things like dash gauges, license plate lights, tail lights, switch gear, windshield washer tanks/pumps, door handles, distributors, steering racks, brake or clutch MCs - were often sourced from suppliers like Jaeger, ZF, Bosch, Lucas, Girling, Carello, Veglia.. the same companies who supplied the big names like VW, Ford, or Fiat.
..and owners of these cars often share the 'interchange' information about where the parts can be originally sourced.
A new windshield washer tank/pump for my Khamsin cost $495 from a Maserati parts vendor.
It's made by Lucas.
I found the parts match those for Jaguar E-Types, and I bought it from a Jaguar vendor for $134.
Door handles are from Alfa Romeo, distributor from a Porsche 928, coil and ECU from Bosch, MC from Girling, Citroen power window regulators.
The steering damper in my Bora is the same as used on some Mercedes and cost me $69, instead of $249 from Maserati.
Door handles and interior ashtray are from Citroen, A/C controls are from VW, tail lights from Carello, side marker lights from a Fiat 124.
Just like Jensen sourced their engines from Chrysler, they sourced other stuff from other manufacturers.
Like its own little eco system.