I think ours is Speedo brand and we got it at Dick's Sporting Goods. It's pink and gray and has both the zipper and the straps and the grab strap on the back. It is neoprene, not the other material. I can't find it online currently. Check ebay.
ETA : It's this one http://www.ebay.com/sch/i.html?_nkw=speedo+infant+life+vest
DD used it for 2 summers and I'm going to see if she can still wear it this summer (she's just about 30 lbs). I like the neoprene vs the crinkly stuff on some other cheaper ones. It has served us well. We took DD in the pool in it to show her how it would hold her head up (baby ones only support baby in a laying on back position). It was comfortable enough that DD slept in it on the boat.
Edit to add: If you want just a floating suit, that's different. If you want something for boat or water safety, you want an approved life vest. Make sure that what you get is applicable to what kind of water you might be in (boating, etc.). I didn't read any reviews but it looks like this is close to the Stearns one that they don't sell anymore. http://www.amazon.com/dp/B006A8FUJM/ref=asc_df_B006A8FUJM...
When we put DD in the lake, we stuck her in a floating ring to keep her upright. in the vest. But for pool time this summer she has a swimsuit thing with inserts that I got at Target.