Do they still make attachments for this track lighting?
Lamps (bulbs) you will definitely find, additional heads you will most likely not. 

That stuff is cheap home center lighting. The type of thing they'll have in stock for a few months and then you may never see it again. That, or they'll get some back in from a new importer that looks similar but is functionally different. Also, parts for things like this are basically nonexistent. If you do happen to find it you only bet will likely be to buy a whole additional set and use just the heads.