Collaboration with frustration

As a new faculty member I am tackling a group of organisms in my research that are somewhat new to me and asking some questions that combine the work I did as a post-doc and a PhD student. Little is known about these buggers, but what is known was almost entirely published by one individual. This person is still at a university, but not really active in research at this stage of their career. By all accounts, the person is very nice and easy to get along with but I have had an enormously frustrating experience dealing with them.
When I first decided on a system to work on as a faculty member I began writing the one person who knew more than anything about them. I never heard back. Four, maybe 5 emails over a two year period and nothing. Then, while writing a grant to pursue the work I ran across an old abstract from the same person's lab suggesting that there was unpublished data out there that would be extremely helpful to me. Again, I wrote. But this time it was different. I received an email back within an hour or two expressing an interest in working together to close out the project that desperately need to be finished up. Great, I thought, finally some contact and I will be able to ask all the questions that no one else knows the answer to. I wrote right back and got nothing. A week later, same story. A month later... etc. Now, 6 months later and a couple of emails (not stalker-level, by any means) gone by, I decided to step it up a notch because of the grant I am in the process of writing and because I am going collecting in a couple of weeks in the same place this person lives. What better time to sit and chat? The email I had received back had two number, an office # and a cell #. I started with the office, but the line goes direct to voicemail. I tried a few more times without leaving a message but never got anywhere. After a couple of days I got up the nerve to call the cell # and basically invade this person's personal space (on the advice of several senior colleagues and a former collaborator of the individual). I left a message on the cell, but the answering message gave a home number. Having already gone far enough to use the cell, I went "full Monty" and called the home number. No answer and I did not leave a message. Feeling creepy and hoping I had properly identified myself in my message, I followed that up with an email explaining when I will be in town and a bit more about the project. That was a week ago. No response.
So, when do I pull the plug and just accept that I am not going to hear back? Do I drop by this person's office when I am on the campus they work on? Thirty minutes of conversation would go a long way to helping me deal with some of the questions I need to answer very soon without re-inventing the wheel, but it seems obvious that the person is not interested in helping, despite their initial email. I am at a loss about what to do next, with only three weeks before my trip.