Standing Orders should be available for public consumption as a matter of routine.
The ICO issues a model publication scheme which ALL public authorities must comply with.
https://ico.org.uk/media/for-organisations/documents/1153/model-publication-scheme.pdf
Since SOs ‘should be’ open source and since you have already requested, but not been given, a copy, you are probably just at the top of a significant administrative deficiency iceberg.
SOs would normally be exempt FoI because they are already open source. If they are not it probably indicates that they either don’t have them, haven’t updated them or are not following them.
Failure to comply with a legal obligation requires a “NO” answer at annual governance and accountability return - would be worth looking at that also.
You could also ask to see the register of FoI requests.
At a guess, I’d suggest you are probably at the beginning of a long road of scrutiny and exposure which will probably end up with you being classified as a vexatious complainer by the PC - that is the usual response to simple requests for access to public records!