The Valve Index is in high demand ahead of Half-Life: Alyx's March 23 launch, but there aren't enough to go around. Because of the coronavirus outbreak, manufacturers in China aren't able to produce enough of Valve's headset, leaving it backordered for months now.
A few weeks ago, Valve confirmed that the Index VR set will be available to buy again in the near future, but stopped short of giving a firm date. Now we know that March 9 is the planned restock. It'll go up for sale at 10am Pacific.
Timing is key here because Valve has already said the restock won't be enough to meet demand. In fact, Valve expects this round of sales to go quickly. It'll be gone long before Monday, March 9 is over.
So, if you're in the market for a Valve Index, make sure to be waiting in the virtual line next Monday, credit card info ready to go, and hope fortune is on your side. Best of luck.