I definitely check this daily in case people need assistance but I'm always available almost immediately on Twitter (@GoldUniGaming) and I have no prob whatsoever assisting. And like I said, if you don't wanna go back, I can easily figure out a way to help you complete the bestiary at a later date, when it's time to be complete has arrived!
So 030 is one of the challenger fights. His name is Thrain, he stands next to the food stand in Cruxis... but he leaves Cruxis after you save Gardenia (which is where you are now).
Entry 039 is Lillia, another challenger event. She's the blue haired elf that stands in the southeast corner of Gardenia. She leaves after you awaken Nolan with the flower, so you CAN still fight her and get her entry in the bestiary.
Do your best to talk to everyone in every town and if you run across a challenger you have a limited time to fight them and get their entry.
Don't worry about going back and getting Thrain... play the game more and when you get to Bardstown and run into the guy with the interest in the Bestiary hit me up on Twitter and I'll see if I can get a fix in for you. Or... email me your save file. My email is gold3nunicorngaming@gmail.com
Do you have a prior save to maybe go back a few fights and do things differently? Do you have a poison spell? The ogres are your last obstacle at the mountain so blow everything you've got and don't fear a boss fight or anything. Let me know if you still can't get past and I'll see if I can't figure it out for you.
In the northwest corner of that cave is a treasure chest with a Fire Scroll. Memorize the scroll and hit the troll with fire. It will remove his regeneration! (If you read the book in Calista's house, it will tell you that) Happy gaming!