To download it you need to go to the Product Download on the Support Site:
1.) select CA Single Sign-On Agent for JBoss MULTI-PLATFORM
2.) Select 12.5 in the Select a Release dropdown
3.) Select 2SP1 in the Select a Gen level dropdown
4.) Click Go
5.) Download the CA SiteMinder Agent for JBoss r12.52 SP1-for LINUX ESD Only package.
The file name is called GEN08181115E.zip and once you opened it it will contain a ca-sm-jboss-12.52-sp01-linux.bin
This file is the right installer as this is the name referenced in the wiki documentation:
https://wiki.ca.com/display/sm1252sp1/SiteMinder%20Agent%20for%20JBoss
You can select a 64 bit JVM even it the installer asks for a 32 bit JVM
Hope it helps,
Julien.