Google for "Turnstile" and "Eggbeater" antennas. Yes, I know they're strange names but you need a particular type of coverage - omnidirectional, low angle and circular polarisation.
I have had some success with only a discone antenna. While I would not recommend it specifically for your purposes, if you already have one up, just try it.
I personally use and prefer a QFH antenna over the Turnstile. However, others have reported liking it. I'm sorry that I cannot point you directly to a dealer or source, but GOOGLE will open a lot of information on all types. Have fun.