Is there an official list of populated systems inside the Colonia bubble?
https://eddb.io/station
Sort by distance from Sol.
Not quite sure, but I think all stations with 21-22KLy distance should be in Colonia?!
Or set Colonia as reference system and sort by distance.
Official? No.
In-game Dr Nagi's advice to use a map filter is an easy way to find them. There are 70 at the moment, if you're wanting to make sure you have all of them.
Out-of-game I maintain the Colonia Census at https://cdb.sotl.org.uk/ which lists all of them (and other aggregated information on the region).