Hi Praveen and Raman,
I am sure that we do not need any coding to populate GSBER if we take it from table BSIK table.
@Praveen: Warning for CI_BSIK include are okay - one is of Enhancement category which you can avoid by adding enhnacement category in to the include from the top menu in SE11 for CL_BSIK.
Now coming to reason why you are not getting any data is because you must have not unchecked the flag 'Field Known only at Exit' in RSA6 changes when you were unhiding the field GSBER.
Please uncheck both flag as shown below.
I just tested it on my system is works perfectly.
One thing keep in mind that after you are done with changes just restart the RSA3 transaction as I did not restarted it and got dump 
But then when I restarted RSA3 it worked perfectly.
Try this and let me know if you face any issues.
Thanks
Amit