I know this is an older thread, but it was the start of my odyssey into finding a plus-size wetsuit so thought I'd share for the next newbie to come along.
I've rediscovering diving now that my daughter is certified (and having spent last summer doing marine research is already a better diver than I'll ever be). Unfortunately, I weight 230lbs now instead of 160, and diving in a men's xxxl shorty in Roatan didn't help my struggle with buoyancy. This year, having been diving more in the last 12 months than in the previous 10 years, I'm determined to gear up with mine own wetsuit. Although I'm still in the shopping phase, one of the first places I found was iSnorkel in Michigan; they sell Henderson Thermoprene 3mm women's front or back-zip shorties in, ahem, *27* sizes, with sizes 10 through 20 coming in both tall and petite. Their size chart covers hip/bust measurements from 30 to 60, with waists 10-11" narrower. Once I find one that fits (instead of being gathered around the waist and loose at the neck like that man's xxxl) I believe it will be warm enough for me down to at least 65 degrees. After all, I have all that natural insulation, and I also like to wear surf leggings/swim capris or a diveskin, as it makes it much easier to get the suit up and over the cellulite.
I'm actually worried that the 3mm will be too warm for Roatan (78 - 82 degrees). Intense on-line research turned up a 2mm from Xcel that goes up to a nominal size 16 (bust 47.5, hips 48.5") and a Bare 14 which is beautifully proportioned but unfortunately doesn't go up quite as large though the hips as I'd like --we'll see.
Active comparison of measurements tells me that Roxy and Bare are the most hourglass-shaped of the off-the-rack suits, with the Bare line going a couple of sizes beyond Roxy. Roxy is primarily a surfing line, and it taps out at about a real women's size 12, but petites might find fits in their line of components (neoprene capris and jackets, for example).
For colder water, iSnorkel offers a Neosport 3/2 up to a 55" bust, with some bigger sizes in petite but no talls. Xcel offers a limited number of suits in their size 16.
Happy shopping, and if you find something I missed please post it here!