Hi,
You may achieve it by using account determination procedure. Maintain a new account grouping code (say ZVB) against 201K in OMJJ - Account grouping code as shown below. DO NOT maintain GL account against the account grouping code against GBB in OBYC. Now, system wont allow to post the 201K movement since it will give account determination error. (Account determination for entry XXXX GBB XXXX ZVB XXXX not possible)
Repeat the same procedure for 202 K movement also.
Note: In this case, system will allow to select the 201K / 202K in MB1A or MIGO, but wont allow to post the document because of account determination error.
Other options would be creating a z authorization object for special stock or using BADI to control the movement type and special stock combination.
Regards,
AKPT