Bishop,
Do you live in SOCAL? IF so you can call your local counties GIS or State Dept of Highways and ask if they have any. I know we have access to our county maps and state road maps for free which are about that size. We even have a city map thats 5 ft by 8 ft that we got for free.
If not, I know they could be expensive (around $100-$200) but you know you would get accurate readings with all of the inputs the gov't uses (parks, highways, rail, airports, etc..)