I opened a new catalog last week. In a rush, I opened new pictures within that same catalog days later.
This is not a problem, in fact this is the way Lightroom was designed to be used.
Now I am unable to locate the original files. Is there a way to pull the originals?
Your first sentence has no bearing on this issue. What do you mean you are unable to locate the original files? Please provide more details.
Here's a guess, that you are looking at the most recent import, and you want to see the other photos ... click on All Photographs in the Catalog Panel on the left of your Library Module.
The original catalog was labeled "Horses"; they were pics of horses. At some time, without paying attention to what I was doing, I opened another set of pics within the same catalog. Now, I do not have any horse pics. Is there a way I can locate the horse pics?
Did you try the suggestion I labelled as a "guess"?
Additional suggestion: especially for beginners, you would want to use one catalog for ALL of your photos, and use metadata (such as keyword) to help you find the photos of interest.