Found these guys...http://www.ondrives.com don't recall seeing them mentioned here before

They do 10x2 LH similar price to MD (£11.34 for 1m) and steel nuts in LH for £5.34 each. They advise steel nuts OK for hand operation and given the level of use I dont see this being a problem (comments?). The nut is 17mm sq and 15mm long so would easily fit inside a (brass?) carrier with a locking screw.

Is this a viable option?