I used my Tabien Baan which I forgot on the day so had to pop back home for it. This error was quite fortunate because, by the time I got back to the DLT, the crowds had thinned out and I whistled through in under an Hour.
The medical cert can be got from your local private clinic for 100 Baht but these clinics, staffed by a doctor from the local hospital. tend to be only open evenings and week ends.