I have a paper which I'm interested in submitting to arXiv.org.
However, the submission guidelines say an institutional affiliation is required for submission. I've graduated in physics from Unicamp in Brazil, but I didn't follow a scientific career. My current employer doesn't relate to physics.
What do you suggest that I do? Is there a way to submit my paper? Or is there an alternative to arXiv.org?
I don't see where it says that you must have a institutional affiliation, Reading comprehension is not my strength.
It also says that you must represent your affiliation correctly. If your current employment is concerned with certain areas of Computer Science or Mathematics (and your paper is in a related area) this will probably count. Otherwise, I'd suggest entering "none", as that is the truth of the matter.
However, I believe that without either an affiliation or a history with arXiv they will expect you to get endorsed before they accept your submissions.
As for finding endorser they write
If you're looking for an endorsement, you can find somebody qualified to endorse by clicking on the link titled "Which of these authors are endorsers?" at the bottom of every abstract.
Now all that is left is for you to convince one of these people that you are serious and competent. Assuming that you were previously affiliated with a institution in the appropriate field you should probably use your contacts there to get in touch with an endorser: they are like to suspect that anyone who contacts them out of the blue is a Not-Very-Serious-Person (tm).