Hello Vachik,
Ideally you should be able to see the service in /iwfnd/maint_service if u have transported all the necessary objects to Production System.
No need to add it again. U just have to activate it.
According to me the reason why u r unable to see the service in /iwfnd/main_service is because some how this is missed while transporting to Production System.
Please try the below and check :
U need to lock the entries of /IWFND/V_MGDEAM (Assign SAP System Aliases to OData Service) in a TR and release to the appropriate system.
The service which u think is missing in /iwfnd/maint_service of Production System, lock only that and release.
Once it is transported, go to /iwfnd/maint_service in the Production System and activate the service.
Regards,
Ashwin