what is the name of this part
You can buy the pin headers with different lengths of pins and pins staked into the plastic to different depths. Quite customizable. 

You can contact header manufacturers and see under what conditions they would sell them with no pins at all. I would guess that for &lt; 1K pieces pulling them out as FM says would be your best and most economical bet, but likely short-lead-time specialist guys like Samtec as @Ignatio says might be amenable, at a price. (Ignore the name 'terminal strip', nobody else calls them that). 



You can buy headers with more than one spacer: 



To pull them out, find a piece of perf board, run the pins through (so the FR4 supports the plastic), and pull them out. If they're too grippy, warm the plastic a bit with a heat gun.