You can probably create symbol library (.lrb) from a schematics (.brd) right inside Eagle PCB editor. You can do that with the ULP programs for Eagle, accessible through the File ► Run menu. Alternatively you can open the library editor and using copy and paste method get what you need.
Convert EAGLE Circuit Board data to EAGLE Library file.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert brd to lbr on Windows
EAGLE is a fully featured PCB design program with over 20 years of continuous development marketed by CadSoft Computer, Inc. It is a easy to learn layout editor available for Windows, Mac OS X and Linux platform. The program is also available in Light version for free.
Convert from brd file
to lbr file
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.