Hi
If I’m not wrong, you can ask for a penal waiver for Oman Police Check in your case as it is not practical to obtain your penal check ( excessive cost etc).
please see this link
Section 5.9
“Consideration should be given to circumstances where the applicant must present in person to apply for a certificate but it would be unreasonable for them to travel to do so due to risk or excessive cost.”
Maybe you can show prices of plane tickets to Oman to show that it is expensive etc and also include evidence ( from the government website or email with the authority etc.) to show that you must travel in person to Oman to get it and explain to the CO and ask for a penal waiver