After the resource redistribution change, Omber no longer spawns in asteroid belts except rarely in Low Sec. So far I have seen Arkenor and Bistot spawn in ore anomalies in Null Sec, Jaspite in Low Sec. but I haven’t seen Omber spawn yet anywhere.
One of the common Level 3 storyline missions calls for 10,000 Omber. I’ve had two missions expire now because I have been unable to find Omber, and I’m unwilling to buy it, since I think the price is inflated due to the scarcity.
If you are going to make Omber so very rare, these storyline missions should stop asking for it. I don’t think the original intent was to make this mission this difficult.