On what page do you see that in the online Area-51 R4 Service Manual?

In the manual, this part is not listed as a separate component. It is a part located on top of each side panel {left or right} it serves to secure the panels.

it is a part of the panel.  you probably can not get just the lock. if it is broken you might have to replace the entire panel.

That's why I'm asking how to find it under what name. It would be pointless to buy a whole panel for the sake of a small lock. If I can't figure out where to buy it, I will have it made, unfortunately it will cost me a lot of time.

You know, the worst part is that the customer who owns the DELL/ALIENWARE product has a problem buying certain parts.

I'm afraid that there's nothing left for me but to have an identical part made { 4 pieces }

agree. I see someone selling a panel on eBay for 50 bucks but it is out of stock.  The panel has triad led and circuit boards inside.  there are possible part number for some small parts of the panel, but even if you know the DP/N, finding a vendor for it may be difficult.

for those interested, Dell nick name for A51 triad is centauri, probably they think it looks like a centaur?  
here is part number for the panel.  I think the left and right panel are identical.  New Dell panel price is 219.99-274.99. Can get a complete preowned case for that much on eBay etc.

If you want to save time, but not necessarily $$$, you could consider buying a spare parts case. You can get a brand new case on eBay for $280 shipped, and used cases are less expensive. Just another option.