Apple School Manager not avaliable

The school that I work for is located in Cambodia. Although Thailand, Malaysia and Singapore have Apple School Manager, Cambodia is not listed as an option when signing up for ASM. Therefore, we cannot leverage some of the best features of our MDM as we have no ASM. Is there another way to sign up for ASM or another tool we can use?

We must sign into each device with a shared Apple ID to install applications. We are unable to link our SIS with our MDM. We need to resolve this issue. Your advice is welcome!