The brands of CMC I usually use are Squires Kitchen and Rainbow Dust (Tylo Powder). You don't have to use the same products as me to get the same results. Go through online reviews of products before you purchase.
In some countries CMC is sold in the form of small granules/crystals (instead of a fine powder). That type of CMC is not suitable for sugar pastes, as it doesn't knead well with the pastes.