Well I made a Revenge Cyberman costume for Comic Con 2008 and Galllifrey 2009. I agree the wetsuit is essential to the look. It's an older style and pretty much can only be had on ebay - modern wetsuits aren't made two piece like that anymore and usually have a lot of logos and designing to them that makes it hard to hide even with a good paint job.
I stand 6' in boots- and I got an XL. I suggest the same for you if not an XXL. Usuallly older wet suits crop up on ebay every few weeks. What you can also do is buy the farmer john style pants seperately and the neoprene jacket as two seperate purchases. This is what I ended up with after my first wetsuit ultimately proved to be too small after painting. So check also under neoprene shirts, jackets and pants too. And hang in there, something will turn up. If you are desperate I did consider buying a bunch of neoprene and having a new suit made like one of the other posters suggested that is if you have the skills or know someone who does. But I'd consider that a last resort.
Also for the Revenge you'll need to modify the lower legs with either leather leggings like I did or use some open neoprene or foam so it creates that sorta straight leg look they had. A normal wetsuit will grip the ankles and be useless here- but ideal for the Invasion variation.
I'd also recommend going for the thinnest (I got a 1-2mm thickness) neoprene you can to help with the heat you'll have in wearing this.
Also remember neoprene is absorbent and when painting this it'll take a few coats to really get it to gleam silver to match the helmet.
How are you doing the chest unit, tubings and gun if you're going after the Invasion Cyberman?
I'm mainly looking to upgrade the shoulder/back cups/discs and find a way to better keep my helmet close din the back panel and maybe if I can find a way to hide it- actually put a voice modulator on the Helmet so I can talk and be heard!
Here's my how-to post from dw_cosplay on how I made my Cyberman in 2007 and 2008 and did upgrades in 2009.
http://community.livejournal.com/dw_cosplay/150843.html
And here's some pics of me in the Cyber gear just last Feb at Gallifrey.
Other pics can be seen here:
http://www.zooomr.com/photos/timelord25/6916064/
And here:
http://www.flickr.com/photos/scottsebring/
http://www.flickr.com/photos/46269571@N00/
And someone got video of me facing off with the Dalek that was there too.
http://www.youtube.com/watch?v=NypoAq7Z86A