Hi
wac1970 welcome to RadioReference
A better antenna would certainly help, however I don't want to make any suggestions that would exceed the cost of your scanner.
What you want to look for is perhaps a surplus or used VHF/UHF dual band antenna, since the bulk of what you seek is in the 150 and 470 to 500 MHz range.
Check the Classifeds on this site.
Another option is to
Google for antenna projects for this range and maybe you could construct one yourself.
Good luck!