Do you want to find all the instances of a block without having to select each one individually?  Well, you're in luck!  PostalCAD has a utility to do just that very quickly.

At the command line enter SBLK.  You will see the opening prompt of "Select block/<RETURN to select by block name>:" and at this point you have two options.  The first option would be to select an existing block with the cursor.  The second would be to hit the ENTER key to return a nice dialogue box listing all the blocks within your drawing for you to select from. 

After you have selected a block using one of the two options a selection set of all the blocks with the same name was created.  Just type in the letter "P" at the next select objects prompt and all the instances will be selected.

For a little fun or to visually inspect the selection, type in FP to flash the selection set five times in a row.