Oof. Honestly I’m surprised it was only three. At least you finally have a paper trail, if you’ve got any insurance that might cover it.
As for the ISP, there’s always the possibility of requesting assistance directly from them, but they probably have internal rules about handing info to non-law enforcement, regardless of the reason.
And if you’ve got some friends who don’t mind backup for intimidation, you could always show up at each workers door, politely introduce yourself and the reason for your appearance. If any of them immediately slam the door in your face or get defensive upon recognizing you (before you tell them why you’re there) then there’s a good chance they know you’re there because they took something.
Anecdote: this happened with my truck in 2019. Someone broke in and stole about $1500 worth of things from a really nice pair of binocs, to the 2000w inverter, and my hand-made bowie knife, and a couple small camping and fishing things. Had to threaten to call the only supervisor I know by name in the police department to get the guy to even take a report for my insurance. They didn’t bother following up with the woman who told me she saw the guy. A few weeks go by and I see someone fitting his description driving the described car, I follow for a bit and he went home. I parked the truck right up in front of the door, knocked, and as soon as he opened and looked past me to the truck he yelled “GET LOST OR I’LL FUCK YOU UP” and that was all I needed to call the cops. After about an hour of waiting someone showed up, talked to the guy, said “well he said he didn’t do it and we never called this woman for a description so we can’t be SURE”
Well lo and behold, a quick glance into his car showed the 2kw inverter under the dashboard, and I was positive I could see the rather distinct custom leather strap of the binoculars under the seat.
No idea who, but apparently someone smashed the guys window to steal a bunch of stuff out of it and they were kind enough to return my items. Crazy how they knew just where to leave them for me to find.
Best of luck in recovering it. Hopefully you get the quick and less… legally/morally ambiguous way.
Truth is denied those who seek it with both eyes closed.