It is possible to get legally married in Thailand and there is a servcie that can help you get married in Chiang Mai or Bangkok. Or just do the Thai paperwork for you, so you can get married elsewhere.
The full Service where you get married legally in Bangkok is the fastest in Bangkok but they a lower cost for people living here in the north and who have the time to wait around for the papers to return and do not mind the slower service due to the cost savings.
Theyhave offered this service for years here in Chiang Mai and Bangkok but they are now happy to take clients who are not just the wedding boutique customers as well. They can also if you go to the bridial shop called "Canna Cards" on wualai road the saturday walking street they can explain the benifets and losses of your wife's rights if she is a Thai national too. You may have seen the signs on the back of Samlours but they are in Thai of course.
Your best bet if you want to register your marriage legally in Thailand.
61 - 65 Wualai Road
T. Haiya A.Muang