I could have sworn I typed in a reply to that thread last month saying you can buy these from etcsupply.com (which I've done on occasion). But I can't find that post now, so maybe it was one of those "I typed it in but then never pressed save or maybe my phone battery died" type things. Anyhow, argh! I feel like I've withheld good info from you guys now.
Anyhow the key with etcsupply.com is putting in your postal code for shipping estimate, otherwise it is something like if you leave it as Canada it will estimate a prohibitive looking shipping estimate and you think "ooh! no way! too much, I'll buy from somewhere else", but it actually doesn't come out in the end as being that high if you just select the lowest cost option in the end.
Anyhow a group order to defray shipping costs is certainly the way to do this and if a store is willing to do it then all the better, I suppose. Guess you don't need this info now. (Poop.)
Although one thing that etcsupply.com can do for you is preinstall a thermal well (basically clear shrink wrap) that will waterproof the probe (they are not really rated to be submerged). You just specify the length. Or you can order it separate (or just DIY something, I guess).