I have checked the IBM website and found SmartSuite and Approach, but there is no information related to the way the applications can be purchased. However, I have contacted a source that has knowledge about IBM applications and it confirmed that based on his experience, Approach can be purchased separately.
Of course, this needs to be validated through the official channels and the best way to do this is through the Contact options offered by IBM: https://www.ibm.com/account/us-en/?lnk=mmi
Note: The link will lead you to the My IBM. Log in with a username and password and then you can contact them.