Hi! The psyllium husk powder can be used instead of xanthan gum. In fact it works better. It keeps the loaf from crumbling apart, and the added benefit is added fibre. So total carbs per slice are 4.6 but net carbs are only 2.3.
You can get it fairly cheap at the drug or health food store. I paid $8.00 for my bottle. Xanthan gum could also work; try only 1/4 - 1/2 tsp for the recipe, although i can't guarantee the results since I haven't tried it that way.