Hello everyone, and help please! :)

[DrS2020]

Hi everyone, I love finding interesting vintage watches at auction and fixing them up - sometimes even managing to do it successfully! I'm looking forward to sharing some of my successes (and failures) with forum members. 

I wonder if you can help with a watch that's more or less finished now, bar one important detail..

I'm looking for a replacement crystal for a 9ct gold Astral watch c.1973. The crystal has an 'inside step'. The inside diameter I have measured at approximately 300 (the part which fits inside the bezel), and I suspect it would be 304-306 outside diameter (sitting on the bezel)? The case is marked 1714/1. I do not have an original crystal, unfortunately, but I did find a similar question on this forum from 2017 which included a photo which I attach - thanks to forum member transporter - which illustrates very well what I'm after.

I've searched Cousins, Sternkreuz, GS catalogues without success, and have contacted a couple of specialists in the UK - and also drawn a blank.

Any advice would be very gratefully received.

Many thanks! 

[KarlvonKoln]

Following.  I also have an old case that needs this kind of crystal.  I wish I knew what kind of watch was in it.