Santanu,
These fields are not assigned to any tables; they only exist in structure/SAPAPO/RELHTC. The data that you may see in a structure can come from non-table sources, and it typically not stored permanently. Structure fields are populated at runtime.
Speak to your local ABAPer, who can explain to you the difference between tables and structures.
Using the tables mentioned by expert Thamizh, a capable ABAPer can re-create in a custom report just about any output that is available in //RELHSHOW.
Best Regards,
DB49