URGENT: How to download Premiere Pro v21, so as to complete a feature film?

After using Premiere for 20 years I have suddenly found myself in a rather difficult situation - a feature film that was edited in v21 of Premiere during 2021 and early 2022 suddenly requires some last-minute tweaks from the director this week.  I thought it would not be a problem - simply open in either version 22 or 23 and hope for the best. Unfortunately - it is a disaster - colour grading is completely messed up, 5.1 channel mixing is all over the place. Not completely surprising as I have been reading of similar issues (very disappointed Adobe with these basic issues between versions -but the post is not about that).

The solution for me was then to simply open it using the version in which it was created - v21.  However, v21 has now disappeared from the CC app (it only goes back as far as 22). I have tried following several links and pages to download "older" versions but nowhere have I been able to find v21.

Yes, I understand it is best practice to try and retain older versions of the apps, and also to not change versions mid-project, rules I faithfully follow. However, a mix of client demands and system changes has meant I have ended up on 22 and 23 out of necessity, without realising the fallback option to 21 would disappear.

Am I overlooking somewhere I can access v21. Can someone please help?