It's a multiple re-entry permit you are looking for, not a visa.
It is surely "easier" to get it at the airport if you are flying out. If you are not flying out you cannot get it there. If you do they will fill in the form for you and to the photo for THB200.
For an appointment at CW go here....https://gov.immigration1.queueonline.net/appointment/appointment.html
You'll need TM8, Photo, copies of passport visa/extension and entry stamps. And it's THB3800.