Answer:
Use a copy machine. They do not need to be originals.
Contact who sent it to you. Most will provide another complementary copy of a W-2 or 1099 for the most recent years (and can do so quickly).
Any older and it may take time, or have a fee, or not be done at all (it is not their obligation to keep files of your records, and their reporting of it was almost always by specialized electronic methods required by the IRS, they did not have hard copies printed). As anything, the older it is, the less kniwn the system is to anyone and it may be a real event to get the data loaded and run to print of one item. (And if the Co or year was done by hard copy, and it is in some box in a storage room, maybe in long term storage (which costs evertime the something has to be found, delvered and brought back) it can also be a big deal.
Many Cos have gone to distributing them by electronic means to you, in which case, they can sometimes be retrieved again by as simply as your logging on to your account and printing it.