How do you maintain networking relationships?

I’m currently 2 years out of undergrad working in a gateway market. I am trying to break into a specific secondary market where I want to settle down long term. I’ve been networking like crazy, holding informational interviews with people and actually getting a pretty good response rate (I have been selectively reaching out to people from my alma mater and/or an affinity group I am part of). The calls usually go really well, but most of the time the firms which the people work for are not hiring. How do you keep a relationship going after that initial call? I don’t want to be a bother to these people because they’re often senior to myself and are definitely busy. What’s your excuse to check in/ catch up with folks after you meet them from an initial phone call?