wanted

[ppppenguin]

You've overthinking this. Just use a washer. Job done.

[Murphyv310]

All you need is a "P" clip.
https://www.ebay.co.uk/itm/125426156758

Not as easy as one think .The Dansette 111 has a 9.5mm F rod and a 3mm bolt.Most screw hole  on ebay P clips are oversized so back to the washer solution or a scrap radio that has ones the same size .Or looking like a strip of plastic and form it with a heat gun

Just use a length of sufficiently wide cable tie cut the length you require. Form it round a bolt of the same or similar diameter as the ferrite rod, warm it a little so you can mold it into a P shape, once done either drill suitable holes or use a thin soldering iron tip.
Plenty of ways to achieve the end result.

In this hobby you have to improvise, so long as the rod is secure that's all you need to worry about. Using a washer is the simplest and easiest solution, I personally wouldn't get hot under the collar trying to get the exact part, IMO you won't!

[boater sam]

A bit of plastic tension strapping off a package, drill hole, wrap around, nut and bolt, job done.