You can track Google GMB map listings in “Snack Pack” and “Local Finder”.
With the “Snack Pack” search option, you can monitor the Top 3 local map listings that are showing in the organic SERPs.
When adding new keywords, tick "Also track Google Snack Pack (top 3 maps) and local finder (top100 maps)", and add the GMB axactly as it appears in Google.
For several GMBs, use a double pipeline in between "||" (GMB#1||GMB#2||GMB#3). Up to 5 GMBs.
Snack Pack results are displayed as in this example:
The Snack Pack box is in 2nd organic position, so the ranks show 2.##:
2.1 - Apple World Trade Center
2.2 - Apple SoHo
2.3 - King Digital iPad iPhone Repair