How to find an arXiv endorser
If you go to a paper on the arXiv (for example, this one of mine: http://arxiv.org/abs/1312.7357), at the bottom, there is a link that reads "Which authors of this paper are endorsers?"  If you click through, you'll see something like 


  Ben Webster: Is registered as an author of this paper.
  Can endorse for math.AG, math.AT, math.CO, math.CT, math.GR, math.GT, math.QA, math.RA, math.RT, math.SG.


which means I can endorse submitters in algebraic geometry, algebraic topology, combinatorics, category theory, group theory, geometric topology, quantum algebra, rings &amp; algebras, representation theory and symplectic geometry.  

Presumably you know of some papers on the arXiv related to yours, so look at their authors.  If you don't know of any, then maybe you should rethink whether the site is a good fit for you.