The only advantage to getting this outside Thailand is if you don't have 400k in a Thai bank account but you must have that to consider the 12 month multi-entry
Go to your local Immigration Office (or the airport if you're close) for them to check your status on the system and get the appropriate stamp (if they can)
You get your Residence Certificate from where your TM30 is filed and it can take anything from 25 minutes (my experience, Sa Kaeo province) to a week or more and can be free (again, my experience) up to 500B. Every Immigration Office is different so there are no general rules.