(author here) This is actually probably the hardest part of the whole thing - finding places to put the equipment and negotiating leases with all the right people.
If it's an actual cell phone tower you're looking at you can usually find it on the FCC website and find out who manages the tower. Most cell phone towers are managed by a third party management company (like Crown Castle or American Tower). The management company can usually tell you if there's fiber although their info is often outdated or just wrong. Even if the tower is owned and managed directly by a cell phone company they are still required to allow you to collocate (FCC!) but they will usually drag their feet through the process - plan on 9-12months and lots of red tape.
As for finding fiber - you can use a paid solution like fiberlocator.com. You can also drive around and look for fiber infrastructure, although admittedly it's hard to recognize if you don't know what you're looking for (or even if you do.) Frustratingly even when you find a company with fiber in the area they usually won't tell you where exactly the termination points are. You can sometimes give them a list of addresses and they'll give back yes/no for each one, though.
I keep track of fiber deployments in Chicago by looking at the city's permit database (which is public and has a pretty usable search UI hooked up to it). Might not be as easy in other cities but I'm wondering if it suggests a general strategy of looking to local government for help in finding fiber. Maybe something as basic as finding the guy who issues permits to dig up streets and asking if he remembers who's been laying conduit recently and where. No idea how well this would work in practice outside of Chicago.
> managed directly by a cell phone company they are still required to allow you to collocate (FCC!) but they will usually drag their feet through the process
No way! Is that only for ISPs or could I get a ham repeater up there if I had enough time/money?
I believe you could put a ham radio up there but it's quite expensive - most tower contracts I've seen are $1200-$2500/month. Also if the tower is already full (at it's structural capacity for wind loading) then you would have to pay for upgrades before you could hang your HAM (which would be tremendously expensive!)
If it's an actual cell phone tower you're looking at you can usually find it on the FCC website and find out who manages the tower. Most cell phone towers are managed by a third party management company (like Crown Castle or American Tower). The management company can usually tell you if there's fiber although their info is often outdated or just wrong. Even if the tower is owned and managed directly by a cell phone company they are still required to allow you to collocate (FCC!) but they will usually drag their feet through the process - plan on 9-12months and lots of red tape.
As for finding fiber - you can use a paid solution like fiberlocator.com. You can also drive around and look for fiber infrastructure, although admittedly it's hard to recognize if you don't know what you're looking for (or even if you do.) Frustratingly even when you find a company with fiber in the area they usually won't tell you where exactly the termination points are. You can sometimes give them a list of addresses and they'll give back yes/no for each one, though.