It does not matter if it is front or back for 26" rims. Have a look at this http://www.tartybikes.co.uk/product.php?pr...;category_id=87 echo one on tartybikes.
Tarty are good. I have dealt with them at least 5 times before. If a product you order them is out of stock and says it is in stock on their website they phone you to tell you so your parts don't arrive and something is missing.
I would go for a hope mono trial. It is a trials-specific brake. Here it is on tartybikes: http://www.tartybikes.co.uk/product.php?pr...;category_id=12 it is £135.