Cantina has such a terrible drop rate, you should just pretend Omegas aren't there.
Anyone saying Zetas are easier to get, don't be ridiculous. You get one Omega for free every day from dailies. Omegas drop as often as Zetas in the fleet challenge. Plus a few more from the mat challenge, GW, TW, and events. Spending all your fleet currency on zetas just means you keep up with the free daily omegas.
We all need more omegas, and we all need more zetas. If you have the crystals, the best places to get extra omegas are the weekly shipment store (10 for 1250), and the special ability mat sale (9 for 1699) that comes about once/month. Also, you can get 1 omega for 200 by refreshing the omega battles that come 1-2 times per week. Save your crystals, and jump on those deals when they pop up. You have to plan ahead to use resources efficiently.