That's a tough one. If you search for shiplap cladding there are similar products. It will be very expensive and you will have to apply a finish to it.
That is expensive and most would agree with me it's ugly as well.
Lots of better options out there. If your going to have slat wall, at least get slat wall that is meant to hang stuff. I have two slat walls in my garage, white however. Its the modern version of pegboard.
I suggest you look at plybead wall paneling. A 4X8 sheet is $27.XX at the Home Depot. And explore local lumber yards that might order you something the big box doesn't carry.
I could be wrong but suspect I am not because I remember even a long while back that it's very expensive now, not that you are not aware of it.
There are so many homes from the 50s and 60s that have it in their basements and some on main levels, you may find someone with a lot of work searching who is removing it to remodel.
(yes I noticed the ceiling too and I think vinyl tile floor)
Knotty pine for sure. A lot of 1960s era basements and some family rooms around here have that, but it's always vertical. If the house has been remodeled once or twice, it usually ends up painted.
Do you have a cabinet shop nearby? Take down a panel and take it to them. Ask them if they can order a custom moulding knife for you, and make you the panels that you need. Custom moulding knives aren't really all that expensive. It may cost you $150 per moulding knife. You may luck out and they may be able to find the moulding knife for the panels you want, already available.