I think the best we'll in terms of finding Yuuka's garden is maybe find somewhere else that used to live in Isir's Cross. Nazrin's probably smart enough to know that she's not going to find anyone who knows the way to the garden, the best we can hope for is eliminating another vector or two. Essentially the choice comes down to a gamble, do we throw the dice in town and hope for a bloom, do we go hunting a bloom we may never find, or do we hope a shrine maiden is better at drawing out something useful from the sword than an actual deity was. At this point, if the person who knows plants says it looks like it has a few years on it, that suggests a bloom isn't too many hours off.
My thoughts are we use the time to secure more funding via seeker jobs, make some contacts along the way, and maybe catch wind of something useful. Also, thinking on it, if we're looking for someone who's visited Isir's Cross and the surrounding regions, the Guild is not a bad place to look. Seekers seem among the most likely to have been asked to range out around there.