The easiest way is to contact your employers. They are used to looking them up. It should not be a big deal.
If your employer is unable to be contacted, maybe it was a small company that has gone out of business, then your only choice is to contact the IRS. This will take a really long time, perhaps 6 weeks or even more.
If you need them to file a return, it may be better to file the return, and guess the amounts and the information. Pay any tax due. At the same time, apply to get copies from the IRS. After you obtain the correct W-2's, file an amended return to correct the info. This way, you'll stop accruing penalties for failing to file.
