How do I get wage transcripts from previous years so I can file taxes for those years

If you cannot obtain the W-2 from your employer, then for a fee you can get a complete copy of a W-2 from the Social Security Administration - https://faq.ssa.gov/en-us/Topic/article/KA-02501

You can get a free Wage and Income transcript from the IRS - https://www.irs.gov/individuals/get-transcript