A trip up and down the bayou is always worth it - you have to look at it as a long term investment.
Collect a business card from each HR person, and use it the next time you stop by. It will get the receptionist’s attention.
Don’t hesitate to get a haircut, and wear a coat and tie to make a good impression and set yourself apart from the others. Have your resume ready, and have a second sheet of paper with all the usual info you will need on an application: reference names and addresses, drivers license number, etc. And have your bags packed and in your vehicle.
If you don’t succeed the first time, if you can, try it again in a month. After a while, the HR people will know you on a first name basis, and know that you are serious.
I got on my first job when I stopped by an office, and they needed a replacement 2nd captain after one was hurt earlier that day. Another time I got on a supply boat when the second captain had to go home for a funeral. This past winter I got on with a good company by knocking on their door (again) and I had an upgraded ticket and GMDSS. So hopefully my knocking on doors day are over.
Good luck to you.