Why are they there.you can see they are buffedup ten percent. Ho o you get one of those makes no sence

I am not sure what you are trying to say there, but the game buffs some monsters to promote them or advertise them. They are on the island so that people know what monsters are buffed and what monsters are not. 4 or 5 of the buffed monsters are permanently breedable!

Ca[n you buy’ one and ifo so how

I dont think you can normally buy them whenever you want but some of them go for sale a lot of times, keep an eye on sales on the right side where events are!