Only one dedicated ski store in San Diego, Ranch Craft Ski Shop. No website, but you can google the address and directions or PM me and I can get you there from where you are staying.
I think Hansens, http://www.hansensurf.com/
in Encinitas might have some ski stuff, but I dont get up that way very often so cant say for sure.
Other than that just the usual big box stores, Sport Chalet, Sports Authority and I think Big 5 might have some ski stuff. Not sure if REI qualifies in this category, but we have them as well.
Let me know if you need any more info.
Hope your day is well.