You can download a non-merged set then delete everything except the 500 games and it should be pretty small. Or you can download the non-merged set and run it against the All Killer No Filler bat file and see how many of your 500 games are included in that. LB is designed to be a front end not the be all end all file manager for your ROMs somethings if you want done in a custom way you have to do it yourself.