Romeo 158 is probaby an MNR unit.
Unfortunately, the way we find out who is affiliated on what talkgroup is by listening to the system.
Since Zone 1 has been on the air for a few years, there's a lot of talkgroups that are now known thanks to locals who have listened to the system and submitted what they hear.
For example, what talkgroup number did you hear Romeo158 on? Chances are you've found an MNR talkgroup. If you had submitted that information to the database, others in your area would have benefitted. What tower are you listening to? What area are you from? What's the strongest control channel in your area and what voice channels are you seeing coming from that tower? What soft id's are you hearing?
I've yet to see much information on the system coming from locals. So far I think Sudbury OPP is on 8576. I was able to figure out North Bay OPP's talkgroup while I was up in Sundridge on the weekend. I think I was listening to a tower around Powassan and I added the voice channels I observed to the database.
Keep a log of any talkgroups you see and any channel designations you hear. By submitting the information or talking about it here in the forum, slowly you and others will be able to figure the system out.