The second series of stamps with provincial seals have been issued on April 2. Same as with the first series, on the My Philately World blog it has the first day covers (Part 1 and part 2), and also the whole sheet. The Thai post details on the sheet is still not existing, they whole new stamp section of their website hasn't been updated for quite some time.
As you can see below, I have this sheet now myself as well - I bought it when I was in Bangkok, and also bought the first series sheets. I only don't know where to get the first day covers, the Bangkok Noi post office did not have them.