Do you know where to find them?

For US shows, searching the Copyright Office website can find them much of the time.

Click red right-most "Search Records" button;
click "Search the Catalog" in left box
click "Other Search Options"; put show title in first 'search for' box; click 'and' radio button; put episode title in second 'search for' box (a few big words together should be sufficient)

You may at this point see a production code, often next to a label like "show #" or "production no.", in the Title field, like for the Knight Rider episode "The Topaz Connection", after Title it has "Knight rider : episode no. 57321, The Topaz connection ".

However, it may just be mashed in with the show and episode title. For example, for The Office episode "PDA", the entry next to Title is this: "The Office : F0717, PDA." The F0717 bit is the production code.

Their database claims to be from 1978 forward, but some mid 70s stuff is in there. And it can take a year for new episodes to get in there, but lately episodes for some shows are there within weeks of broadcast.