I need a transition that goes from SmallCave to farmhouse basemant. I think there's something like that ingame, but i can't be sure.

i don't think there are any, farm pieces are not very variable.

for basemants, the only one that could be interesting for you's maybe some, uh well entrance thing, guess if you filter all to *well*ent* should get it.

all others i remember either don't have actual openings or are parts of bigger models (whole house slices etc)