No matter what the UY and contract size you are looking for it is the one you can't find much or any of.

If you're looking for OKW that is one resort that actually had points spread out relatively equal across UY's so no, March isn't going to rare but sometimes it is just waiting for the right option to come along. What happens with OKW though is that being the first it's typical for contracts to be in the 150-230 point range and smaller contracts than that are more rare but I'm not certain what size you're looking for.
SSR is very large and I think also a decent distribution across UY's but still might be waiting for the right one to come along.
From all you mention I lean towards the thought that OKW could be the best add on for you. It will be a bit more in the long run that SSR but since GV's or larger villas are in your mind I think that swings towards OKW. And the same UY makes it easiest.