I love this question. I think you got a lot of good advice around setting calendar reminders for regular check-ins over email and connecting over LinkedIn.
If you will be in the same locations as your co-workers, I'd recommend going a step further and meeting up for coffee every few months. Sometimes meeting face to face gets us out of everyday distractions and can be more memorable than an email.
On LinkedIn, writing posts and sharing articles is another great way to update others. For example, you may pose a question about an article you read or share an update about recent community service event.
Lastly, spend some time preparing for these interactions. Think of specific questions you could use an outside opinion so you use their time effectively. Make it a two-way relationship; look areas you are an expert or have a unique perspective.