In laboratories, this would be incorporated into the Chemical Hygiene Plan.
Either way, if you regularly review your inventory so as to use up or dispose of chemicals older than say, three years, you are likely to never encounter this problem.
If you are not using an SDS software package or SDS supplier who can assist you, start by figuring out what happened to the company. One resource that might work is the Internet Archive's Wayback Machine which preserves snapshots of web sites over the years.
While many companies go bankrupt, their assets and product lines are usually acquired by other manufacturers. If you know or can determine the web site of the company, enter that in the Wayback Machine and you may be to browse your way, for example, to the MSDS's that Solutia had in 2004 (they were bought by Eastman Chemical in 2012).
Also see our FAQ entry What are my rights to an SDS?
You may have MSDS's (rather than SDS's) that were created prior to the implementation of the HCS 2012 (see "What are Safety Data Sheets and Safety Data Sheets (SDS and MSDS)? There is no need to go through your collection and find SDS's for materials received prior to June 1, 2015 - but as you receive new shipments of those older materials, you will need to update your SDS collection with the new sheets. Under the OSHA Haz Com standard (HCS), manufacturing employers were not legally required to obtain, maintain, and make available upon request copies of MSDS's until May 26, 1986; see this official OSHA interpretation "MSDSs for chemicals purchased prior to 1985".
If all else fails, see if you can find an SDS for an identical formulation from another manufacturer (see "Do I have to keep every SDS that I receive?
The big issue is what to do when the manufacturer has gone out of business or merged. OSHA has confirmed that manufacturers who are no longer in business or who have discontinued a product line do not have to provide SDS's.
If you are looking for the SDS because you have the material in your current inventory, one might be tempted to simply use it up to eliminate the need to have the SDS.
However, you still need to document your company's use of that material under .1020, Access to Employee Exposure and Medical Records, and the SDS is normally the easiest way to do that.
That really depends on how SDS's are handled at your organization.
If your employer uses a software program or Internet subscription service for SDS's then maybe not (check with your supervisor, the answer depends on what state and federal agencies have jurisdiction, see also the section on paperless compliance below.).
See the OSHA Interpretation titled Hazard Communication Standard and Material Safety Data Sheets.