Finder has some excellent tools for searching that a lot of people seem to be unaware of.
You can basically search for anything.
For example, you can search for files bigger than a certain size - which seems to have been your question - very easily. Also, any search that you may want to repeat later can saved as a smart folder.
Here is an example:
- press Command-F and set your search like this; of course, you can search starting with any folder you like (I started this on the Desktop), or search the whole Mac (just click "This Mac")

You can combine a huge number of criteria to set the search as you want it (file name, extension, kind of file (image, audio, etc), date of creation or modification, and so on and so on. You can use Boolean logic such this and that but not such and such, etc....