I used to board my horses in Fallbrook. Grass hay of all kinds is available out there. Call ahead to the feed stores to find out what you can buy and for how much. If you'll be boarding, contact local stables and secure a spot NOW and find out what they feed.
Be sure to take 2-3 bales per horse of your current hay with you, and a bag of grain for each horse. You want to make diet changes slowly, over 1-2 weeks minimum.
I used to feed Bermuda and Alfalfa hay, half and half, and didn't give any grain, just a vitamin supplement in a little beet pulp. Most horses will do fine on Alfalfa, if you introduce it to them slowly.
Keep in mind that bales of hay in California are much heavier than bales in the South and South East, 100-125 lbs for Alfalfa and 70-90 lbs for grass hay. You'll want to weigh out what you feed now, or approximate the weight you feed per day based on the average weight of your bales and the amount of the bale each horse gets. Keep a feed diary so you can keep track. When you get to CA, feed half your old hay and half the new hay (until the old hay runs out), keeping the weight the same as you were feeding at home.
Alfalfa is much more nutrient dense and higher in digestible energy, so you'll feed much less of it than of the Bermuda or grass hay. If you normally feed 20 lbs a day of Bermuda and you decide to feed half and half, then you'll be feeding 10 lbs of Bermuda and 6-8 lbs of Alfalfa (depending on the cutting). Does that make sense?