You are going to have a great summer down here in America's Finest City. Some sites you way want to check out include the following: Craigslist, Backpage, SignonSanDiego, UTSanDiego, Trulia. Perhaps you could do a "key word/phrase" search such as "seasonal rental." One not of caution though when using a few of these sites as there are, unfortunately, scams out there so do NOT wire/send your money to anyone online.
There are other things I might try. Perhaps you can come down for 1-2 days and walk around the area you'd like to live and you will probably see some for rent signs/postings.
As a professional agent, I do have access to some additional sources and would be happy to utilize those avenues for you as well in the event none of the above works.
All the best and have a blast here this summer!
Chad Basinger, REALTORÂ®, CPA, CFPÂ®