Agents won't help with this. Professional agents (real agents) generally only sign acts or artists that are ALREADY making money. They won't work on hope. They will take on people already producing income, because they get 10% or 15% or whatever is standard or negotiable. I could be wrong, and hopefully someone will correct me if I am. But, I am pretty sure that any established agent, will only take on proven artists, established and working already.
Businesses use marketing firms for their commercials. It is the marketing firm that you somehow need to get in with, since they are the ones that will be contracted for each project.
In the past, and I assume it may still exist today, there were music houses, with on-staff writers for songs, commercial music, whatever.
Independent contracting, most certainly occurs though. Many years ago I had a friend who made his living doing jingles, but I can't remember if he was staffed in-house, or subcontracted. Too bad I don't know him anymore.
Companies like
www.taxi.com charge a yearly fee, and they will submit music they feel worthy to enumerable projects, like licensing for tv shows, movies, ads, everything. They are legit, but I don't know the ratio, of paying to successful placements. Hit the boards to find out success and horror stories.
Keep in mind, that sometimes exposure is worth more than small change initially. I know Moby, though successful, maintains a free download site for his music, for non-commercial projects and shorts. He might consider it a labor of love, but it keeps his music out there.
http://mobygratis.com
Wish I could help more. Jingles are something I've considered over the years, but never looked into seriously.
but i bet that song would go well with like H&R block commrcials ....especially right now with it being tax time.....just an idea....a very doable idea...go an agent? 
