you can register at the IRS website and then see if transcripts for those returns are available online.
https://www.irs.gov/individuals/get-transcript
or you may try calling the IRS at 800-908-9946
finally, you can submit form 4506. the IRS is supposed to keep copies of tax returns for 6 years but not all those years may be available online. 2014 may no longer be available anywhere.
https://www.irs.gov/pub/irs-pdf/f4506.pdf
