My estimate is that 35 drops in Silver Seas are about 5%. Assuming this is true, on average you should get one 35 drop for every 20 kills. Also 1 in every 20 groups will get lucky with a 1/1 and there will also be groups that go 0/60+ on a particular drop.
Over time it should all average out, but strangely this does not seem to be the case. After more than 100 runs in this zone, the group I go with has 12 usukane 35 heads and 0 Skadi 35 gloves. I hear that another group on my server has 0 usukane 35 heads and 8 Skadi 35 gloves.
Do both of these groups simply exist out on the extreme edges of the bell curve or is there something else going on (moon phase, enter time, group size, path, kill order, cell usage, ability usuage, people/items unlocked) in Silver Seas that is influencing these results?