One potential method would be to generate a list of all the blocks in your Simulink model, and then find blocks which are of the type 'TriggerPort'. From there, you just need to determine the parent block of the 'TriggerPort' which gives you the Triggered Subsystems that you are looking for. You can accomplish all of these operations programmatically via theget_param andfind_system functions.
Here is a quick little example script that performs the operations that I described above. Thefind andstrcmp functions are used to determine which blocks are of the type 'TriggerPort' from the blockTypes cell list.
% Generate a cell list of all blocks in the current Simulink model
blockList = find_system(bdroot,'Type','block');
% Generate a list of the block types
blockTypes = get_param(blockList,'BlockType');
% Find all blocks with trigger ports (enabled subsystems)