How do I obtained money vested in companies I haven't worked for in over 25 years
Will I be notified by the company around my retirement age letting me know I have
Money vested or do I have to contact the companies

Do you mean you bought shares in companies you worked for over 25 years ago? To my way of thinking the shares are still yours, but did you get actual numbered share copies ? I would suggest calling someone at those companies. Maybe your interest has been revoked because of a time lapse.

I think you probably have some money (either in the form of shares in stock or mutual fund or perhaps as cash) stashed away in a company managed retirement account.

If I were you, I would find details about these securities I hold - for example, I would find details about how many shares of a stock or mutual fund I hold in XYZ company's retirement account. I would then go to fidelity.com or vanguard.com (or any other online brokerage) and open a roll-over IRA and roll over funds/shares from these retirement accounts to this roll-over IRA. Once you have all these bits and pieces of vested amounts pooled up into this one roll-over IRA, you should have no concerns.

How your vested amounts are treated by these companies varies from plan to plan. There could be plans where they maintain your account till your retirement and then inform you (although I highly doubt this would be the case) but there could be companies where they liquidate your funds and post you a check after deducting all penalties. I know of companies that give their employees 90 days to roll these funds over or they send you a check.

So you would need to call the HR from these companies and ask who they do their retirement plans with. You should then contact the retirement plan maintenance company and find out the company policy - this way you would probably make the best use of your time and not end up explaining your scenario to a bunch of folks at the companies you worked for in the past.