Whether from an online store, a building about to be demolished or gutted/repurposed, or something else, where should I start looking to expand my collection?
Those are both good possible places to look for alarms, though it depends.
You could also try thrift stores, but I’ve never had any luck with those in my area… Maybe you’ll have better luck.
If you have a Habitat For Humanity ReStore in your area, check their electronics section. They often get commercial electronics and hardware, including fire alarms. I’ve gotten a few from there, and sometimes they have older stuff.
As for getting them from buildings, that’s a bit tricky, as you’ll have to ask whoever’s working on it before you can get inside and salvage them. I have some recent experience with an old school that was being prepared for demolition, and it took a lot of calls with the company to get a day set up for that. I was lucky enough that they were even willing to let me inside in the first place. The name of the game is timing, and it’s best to get your foot in the door early.
You could also try fire alarm system contractors, as it’s right from the horse’s mouth. You’ll have to find out what companies are in your area, and if they’re friendly to enthusiasts. They’re usually very business-oriented, but if you meet the right person, you could score some alarms from them. It depends, though.
Getting alarms from an online store, such as EBay, is probably your best bet. However, you’ll have to pay a pretty penny for some alarms, especially if they’re highly sought-after. (e.g. the ever-elusive Simplex 4050-80 light plate.) I get a lot of my alarms from EBay, personally, but there might be a few other online stores that sell alarms.
eBay is my go to. When I worked in the field we’d occasionally pull out old things that I would be able to take home with me to save them from the trash. Sometimes they’d work, other times needed small repairs, and some were duds. Could always reach out to service companies around your area, introduce yourself and explain that you want to learn about alarms. That you’re wondering if they have, or could set aside, some devices that would otherwise be tossed out for you to tinker with.
I’ve personally never had success, but some people have found items at a ReStore or Goodwill.
eBay is the go to. It has different alarms at a reasonable price. Auctions you can win for cheap. I have gotten System Sensor devices for less than $10. Totally worth at least looking.
I just usually trawl on the local classifieds (Leboncoin in my case) or eBay. But in some rare instances I managed to find devices in yard sales, albeit this is more an exception than the rule.
I buy my stuff off of ebay
I usually look at eBay, FB Marketplace, and OfferUp.
I usually buy all of my fire alarms from eBay. There are some other retailer sites but I am not sure about their reliability because I’ve never used them before. They may be expensive but it’s acceptable for me.