There are a few ways you can go.
You can get the block table record of the block you want, and then use the method ' GetBlockReferenceIds '. This will get you all the object id's for all the inserted block references.
For the current space, you could use a selection set, and filter for the block name and the current tab name.
You could use a selection set, and filter for just the block name, and get all the block references in all spaces for said block.
You could step through the layout dictionary, and then each layout's definition, and grab the blocks yourself filtering as you want.