For Ditra, I need about 100 Square feet... - about 30 linear feet. How can I order that?

Yes for Ditra you can order in ln ft here: https://www.masterwholesale.com/schluter-ditra-ditra-xl-uncoupling-membrane.html The cost listed is per 1 ln ft. just put as many ln ft in the cart as you need and we wilol ship to you.