For un-restricted access you can see all SRD belongs to the user company which you have added in the Access Restriction table.
Coming to the Entitlements issue:
For "Company A" users create an Entitlement group in the Entitlement Console(Open this console through Object list and Type Entitlement Consol in text and press enter u see the form name called: Entitlement Console) and add all Company A users in that group.
So now for which SRD's u want visbile for the Company A users then add the above group in the SRD Entitlement Table.
Now check the issue and see the results.
The same procedure can be applicable for the Company B users also.
For more information you can also see the SRM Configuration and Administrator guide.