Have a Tax Question? Ask a Tax Expert
The easiest way is to get IRS transcript. It will take you about 15 to set up your account, but your wife will have to get her own. https://www.irs.gov/individuals/get-transcript
Transcript looks little different than actual tax forms but it will have all information you will need to prepare your federal tax return.
That's the only way. You can request your transcripts over the phone but it will take few days to get them. The IRS will also fax transcripts to registered tax professionals but not individuals. Using the link I provided you can have your transcripts within half an hour.
If you owe any taxes, you are already late. Extension is only for filing, not paying.
If you are due a refund, it does not matter if you miss the deadline because all penalties and interest is calculated from balance due. If you do not owe anything, there will be no penalties, even if you file in December.