It is installed as a component when installing Adaptive Server Enterprise PC Client. You will need to download PC client set up from the spdc(https://sybase.subscribenet.com/) or get the pc client cd. Please see a capture from custom install of pc client for 15.7. You will see Sybase central checked in the window hereby.
Not sure which version of SAP Sybase ASE you working on but SAP Sybase has been asking us to move over to SCC for some time. SAP Sybase Central plug in support will be pulled away pretty soon.
http://www.sybase.com/detail?id=1099112
I am not sure if the pc client is available for some one to download if they do not have a spdc support id. Probably some one else in the community can enlighten us about that.
warm regards,
sudhir