Paneling and Trim - Paint-Grade T&G Paneling

I'm planning to hang T&G paneling on an interior wall and intend to paint it. I'm looking for paneling that is about 7" wide to match existing paneling that I have on my ceiling. The only stuff I can find at Home Depot or Lowes is pine that has a lot of knot holes and other flaws that would need to be patched up in preparation for paint. Is there paneling out there somewhere that is already paint-ready? I found pre-primed 7" MDF paneling at Lowes, but it has grooves down the center of each plank which makes it unsuitable for my purpose.

I assume you are wanting T&G boards and not paneling. Try some of the local lumber yards - they should have a better selection than the big box. You will pay a lot more for clear wood - no knots.

Yeah, T&G boards. Sorry if that was unclear. What I am really hoping to find is something made from MDF since I'll be painting it anyway. I don't want to pay for stain grade.