There are mods that double the vanilla spawns and reduce the respawn cooldown. Right now you need to hope that the spawned ones are good or wait and rare spawns take forever to be one of those two dinos. Would make those more accessable to most of the people on the server too and highers general pvp at osds and veins by doing that.
#Higher carcha/giga spawns
hallow raven
crisp mauve
Center respawns a gig or carch as soon as one dies, I just farm them there till I get a good one