I'm starting to get into licensing my music to international libraries as well.
As far as I can see, there are too many libraries out there... Only a few are worth your time and fewer pay decent money. There are exclusive libraries, non-exclusive libraries, some pay money upfront, some don't. Some pay for sync events, some don't.
Also, it seems to be VERY HARD to get into the GOOD and worth libraries.
If you manage to get your music into some of those, I don't think you'd need an agent for this, since they will do that work for you (for a price, depending on the library). All you need is to shop your music to these libraries, get accepted in as many as possible, and let them place your music for you.
Now, if you
do know a good agent who wants you, I'm sure he could get you other great placements, so you could also work with him. The more chances of placements you have, the better.
With the Mexican TV shows I've been writing for, I've been lucky that they sell them all over the world, so for this music all the licensing becomes "automatic".
But I really want to get all that music (that I already have and aired) in those libraries to make even more royalty money from those same tracks. Otherwise they wouldn't be used for any other shows... A waste!