The online rooms on GT5 are different everyday, most aren't planned out days before so you will have to look for a cruise room yourself at the time when you want to cruise.
There's several threads about cruise rooms in the clubs & leagues section, and I'm pretty sure I've seen cops & cruise stuff sometimes posted in the "spot races" section - which is particularly for impromptu racing, or just single events people have on fairly short notice https://www.gtplanet.net/forum/forumdisplay.php?f=12
Have a good look through those sections. Sometimes it takes pouring over several threads, but it's worth it when you find what you're looking for.
