I found mine at Home Depot in the door hardware/lock section. Cost maybe 5 bucks or so as I recall.
 
I got the keyed mag switch from Vans. It came with at least one extra lock. Fit the hole exactly.

Karl
 
Mine is one of the Home Depot types that I happened to have in a drawer when I was getting ready to rivet the door together. It works fine (I did change the cylinder out once because the key broke in half while I was wearing in the latch dogs), but I wish I'd taken a deep breath, stopped work and gone out and gotten one of those cylindrical key types from a locksmith. It's too late now, cause changing out the housing would be pretty tough!

The only reason I'd go with a different type is cause it would look cooler - the HD one works fine.

Paul