There IS new old stock out there (NOS), but generally speaking, it's been hoarded by sellers who know that later on they can charge 200% for a component if somebody needs it for an existing system because even paying twice the price for it, when they NEED it, is less expensive than a whole platform upgrade. Ebay generally has just about anything you need for just about any generation you need it for, from somebody with some NOS, but it won't be cheap usually.
Now used hardware, different story. That can usually be had for reasonable prices BUT as with anything used, you are rolling the dice and the only way to minimize the risk is to buy from a very reputable seller with MANY sales in their history. Even then, it's never a 100% guarantee that you won't get a lemon. Often though, sellers will work with you to make it right if there is a problem but you can't count on that in every case so as before, it's always some amount of risk involved.
Even new old stock could be risky because things like capacitors still age and degrade even when unopened and sitting in the box for years.