I have a beautiful pair of antique spirit slates in need of a new flap. Any recommendations for where I can get the right size cardboard?
Michael's? Or has someone happened upon the perfect kind on Amazon so I can have it delivered to me?

Use flat black matte board from any framing shop. The key is to use the kind the is has a black middle layer so you have solid black through the whole flap. Probably also available at Michael's or Hobby Lobby. Find it in the custom framing department.

TEB3

Thanks. And those that come in a standardized thickness, or are there options there?

They are made in a number of thicknesses. Think of paper and the pound weight designations. Now the thing is what a particular store stocks. Why don't you just Google "black core matte board" or something similar? You'll find your answer as to who manufacturers it and then who sell the particular kind you want.

TEB3

I make aluminum flaps 1/64 inch thick that mimic chalked slate quite well. They should last as long as the slates. PM me if interested.
Marc

I agree , I have some slates from Marc and they are perfect.

I have two sets of Marc's Slates and can attest for his craftsmanship. Plus, Marc is a really interesting and nice guy to chat with at ECSS.

Thank you, gentlemen. Happy to hear the work is appreciated. And looking forward to Myrtle Beach this coming year.