Big Lake is in Sherburne Co, which still uses conventional VHF. Their frequencies should all be listed in the RR Database under Sherburne Co. It's also right on the border with Wright Co, which also still uses VHF.
You might also try listening to fire dispatch from Anoka Co (154.280) and Hennepin Co. (154.385) These counties are digital but have their fire dispatch patched to VHF. They will be more active since they are more populated counties in the metro area.
Also, just FYI...Having a scanner in your vehicle is illegal here in MN unless you have a ham radio license, so keep it well hidden if it's in the car, preferably in the trunk with no batteries in it.