So starts the research for peiod warp thread materials...

With weaving, especially on a weighted loom using hand spun wool, the kind of roving/wool used is very important.
Why? It's simple - stretch.  Short staple (the length of the fibers) stretch.  It's great for things that are knitted, crocheted, or even Naalbound, but not for weaving.  For weaving stretch is not a good thing and adding weight just makes it stretch more.
So what I'm looking for is a long staple wool, from an unaltered breed.
Unaltered breed - what's that you say?
Well, as you may or may not know, people like to tinker with mixing different breeds of animals together to produce an animal that is better suited to their needs.  This is normally not a bad thing, however, for the purpose of authenticity, using an unaltered breed is the best idea. (i.e.Anglo-Saxons would not have has access to wool from a sheep that didn't exist until 1847 :)
Lucky for me, England is actually into preserving unaltered breeds and ordering my roving is now just a few clicks away...Yay inter-webs!

Here is a website that I found that carries roving from unaltered breeds here in the US:
http://www.spinderellas.com/lwsheepbreeds.html

For my purpose I may use this one:

Cotswold originated in the hills of Gloucestershire, England from indigenous stock and is one of the oldest breeds known to us. It has contributed to the ancestry of other breeds in UK and Europe. It is large with a white face, wool on the legs, with a characteristic lock of wool on the forehead. Cotswold sheep are noted for their long, strong fiber, with lustrous natural wavy curls.

• AVERAGE FIBER DIAMETER
  Micron 33-40
  USDA Wool Grade 36’s-46’s
• GREASE FLEECE WEIGHT Ewe 12-15 lbb - WASHING YIELD 60%
• STAPLE LENGTH 12-15" - though many are sheared twice a year.