you should be able to get it at cyclocross world.com
I've used Velox JANTEX tape and it performed flawless for me. 1/2 the price of the stu thorne stuff.
The link I posted above is the Jantex as well, I've got several wheels set up using it, no problems at all.
The Thorne tape is sold at cyclocrossworld.com. Great stuff! Be careful what you wish for, though. I have a set of tubulars(road) and used the 'Belgian Method." I got a flat; even though I had a spare, I could not get that tire off - not even a tiny bit. I finally had to use a heat gun and a pair of channel locks at work. By the way, it was the front tire, and the Cafelatex sealant didn't work. The tires were Challenge Parigi Roubaix; the best tubulars out there. But unless you have a mechanic to f**k with the tires/wheels, and are prepared to walk home when you get a flat, store up a big pile of karma. Tubulars are worth the initial effort, and even I can feel the benefits. But when they go bad, unlike Mae West, they don't get better.
I have found that you HAVE to take them off annually to guaranty that they will come off. Once the glue sets up hard they are a PITA. For using sealant, the best combo I have found is Stan's in Clement PDX's. No tubes in no tubes ... ;)
If you are using carbon rims, tape is highly recommended. If they are Aluminium then glue is fine. To remove a tire that has been taped is hard. A small screw driver can be carefully inserted under the tire after you work it loose a bit. Then you can roll the screwdriver to free the tire. Takes a bit of time, but if done carefully you will not damage the tire or rim.
Or use tire lever - takes a bit more work to get started but less risk of damage.
All the tape does is take up space and add gluing surface. If you have a wide rim and don't run sub 20# you can probably not use it. I have seen rolled tires that were taped so there is a lot to be said for just doing it right.
+1 on not using tape on aluminum rims. Layer the glue correctly and you don't need tape. More than likely your tire will fail before your glue job if you glue correctly.
It's true, tape is not necessary. The purpose of it is to substitute for several layers of glue, which makes the whole gluing job take less time and be more convenient. Tape is worth 2-3 coats of glue, meaning you only need an additional 3-4 on the tire & rim (combined). If you glue a 'cross tire without tape, you generally need a minimum of 6 layers total (direct quote from Tom Hopper, who used to work for a 'cross team I coached, now he's Jeremy Powers' mechanic). So the tape is mostly a time saver. I've raced on pure glue jobs as well as glue/tape, and never rolled a tire, but I've used tape the last couple years as a time saver (I have 4 sets of 'cross wheels and not a lot of extra time).
This is a good instructional piece on gluing tubulars for 'cross, BTW. Zanc goes through why he does each step, so you understand why each of them are important.
As to whether to re-purpose a tubular wheel between cx and road, it's definitely possible...but it's also a lot of work. Road tires only require 2-4 layers of glue to be well glued, anything extra only adds rolling resistance. Tape definitely adds rolling resistance, due to the "sponginess". Testing on rollers has confirmed that. So then you're looking at not only peeling the tire after 'cross season (and likely ruining the tire if you did a good glue job), but also removing a lot of glue just to make the rim suitable for road tire use. For most of us, it's easier just to have different sets of wheels for road and cx.
Gluing using cx methods is overkill for the road, BTW, as the earlier poster found out. Makes it nearly impossible to remove the tire, which you really need for 'cross, but you don't need on the road (where higher pressures and smaller casings result in tires staying on rims much better).