Here's the 'comments.py' router file with the specified endpoints:

```python
from typing import List
from fastapi import APIRouter, Depends, HTTPException
from sqlalchemy.orm import Session

from app.api.v1.models.comments import Comments
from app.api.v1.schemas.comments import CommentsCreate, CommentsResponse
from app.api.core.dependencies.dependencies import get_db

router = APIRouter()

@router.get("/commentss", response_model=List[CommentsResponse])
def read_commentss(db: Session = Depends(get_db)):
    commentss = db.query(Comments).all()
    return commentss

@router.post("/commentss", response_model=CommentsResponse)
def create_comments(comments: CommentsCreate, db: Session = Depends(get_db)):
    db_comments = Comments(**comments.dict())
    db.add(db_comments)
    db.commit()
    db.refresh(db_comments)
    return db_comments

@router.get("/commentss/{id}", response_model=CommentsResponse)
def read_comments(id: int, db: Session = Depends(get_db)):
    comments = db.query(Comments).filter(Comments.id == id).first()
    if not comments:
        raise HTTPException(status_code=404, detail="Comments not found")
    return comments
```

Explanation:

1. We import the necessary modules and dependencies.
2. We create an instance of `APIRouter` for our comments routes.
3. The `read_commentss` function handles the `GET /commentss` endpoint. It fetches all comments from the database using `db.query(Comments).all()` and returns them as a list of `CommentsResponse` models.
4. The `create_comments` function handles the `POST /commentss` endpoint. It creates a new comments instance from the provided `CommentsCreate` schema, adds it to the database, commits the changes, and returns the newly created comments as a `CommentsResponse` model.
5. The `read_comments` function handles the `GET /commentss/{id}` endpoint. It fetches a comments by its ID using `db.query(Comments).filter(Comments.id == id).first()`. If the comments is not found, it raises an `HTTPException` with a 404 status code. Otherwise, it returns the comments as a `CommentsResponse` model.
6. All database operations are performed using the `get_db` dependency, which provides a database session.

Note: This code assumes that you have defined the `Comments` model in `app.api.v1.models.comments` and the `CommentsCreate` and `CommentsResponse` schemas in `app.api.v1.schemas.comments`.