Hello,
For my wedding anniversary, me and my husband will travel to Indochina with emphasis Vietnam for around 10 days (or more). Look for somewhere romantic and fascinating. Thanks.

If you're interested in Vietnam, consider Halong Bay, Hoi An, Nha Trang or Phu Quoc - best destinations for couples with beautiful beaches. October is the autum in Vietnam so the weather is so nice. Hope you have wonderful time with your beloved.

10 days is not a long time so you should take the multiple tour like Vietnam-Cambodia (about 4-5 days, often depart from the Mekong Delta), then you can back to Vietnam in the rest of time. Danang and Nha Trang in the Central are highly recommended

How can I refer some multiple tours? Any suggestions?

asiapackagetravel is one of the best travel agencies which you can consider. Visit their website for further information