I have recently started working as photographer of architecture, without any previous background in the field (no relevant studies, not someone's assistant, no architect friends), so I need to do a lot of cold calling too. Here's what mostly works for me, hope it's of some use to you.
When calling, I always ask to speak to an architect and, if he is a name, I ask for the architect in charge of the office. I try to chit-chat about a recent project of theirs that I liked (but no faking!). Then I emphasize my focus on architecture, using language that the architects understand, knowing that the person at the other end gets it. That helps break the ice and helps people remember me. Also, when I send in my portfolio, I can attn: it to them.
I follow on all the competitions, awards, talks, events, etc that I can. I note who is being active at the time and later call them, initially talking about the awards, etc. as the reason for my calling. I usually offer to re-photograph their work in my way; this sometimes leads to a commission, but for less than normal prices. Even if it doesn't, I try to arrange a shoot for myself and then contact contractors, builders, and specialists that worked on the project. And always make sure the architects see the photos.
I am also interested in photographing construction sites as my personal work and have tried to arrange that several times. On one occasion, where I also delivered small jpegs of the shoots to the architects for free, I was later twice commissioned from them, and more are on their way. So, I try to be open and flexible and never pass up an opportunity to put my name and photos in front of their eyes. Maybe this cannot work for you, but sometimes giving up a little of your time and money can be profitable later.
Oh, and what I have found is that, while most of the architects are struggling right now, a few are very prolific and are in fact hiring to keep up with the workload. And usually they also are very active on social media.