There are maps online but its really not that great from what ive seen anyway.
If i were you id make my own, however the map maker is just as good as the in game one.
In game you can choose what planets and stars will show up in game, quickly pick the distance and other random levels and be playing a map with 250 planets in 5 mins.
Using the DL map maker i had nothing but crashes so i use the in game one, but that may be my issue alone...
Unless you really need the galaxy to spell out ure name, or something odd like that... i vote in game maker

is there something you are looking to make? note the option for random colony planet will make every random one useable in terms of expansion.
-SiN