This is a good question. I also like to have copies of the Vedic scriptures without commentaries for self-study and recitation.
There are a few publishers available who publish the Samhitas and Brahmanas in the mool form.
If you are in Europe you can buy the texts from Bibliotheca Indica published by Biblio Verlag Osnabrueck, Berlin. They have a full collection of the Samhitas and the Brahmanas (I think volume 71 onwards). These books are the reprint of the Bibliotheca Indica which was published a few decades ago by the Asiatic Society Bengal.
If you inside India, there are many possibilities. The first is Chaukhamba Indological Studies Delhi or Varanasi. They have all the Samhitas and Brahmanas in mool form (see page 27 onwards in the link).
Another option is to get the texts from Vishveshvaranand Vishwa Bandhu Institute of Sanskrit and Indological Studies in Hoshiarpur, Punjab India (Vishveshvaranand Institute Publications).
Also, Vaidika Sansodhan Mandal, Poona and Sampoornanda Sanskrit University in Varanasi also publishes some Samhitas and Brahmanas in mool form.
Finally, there are some publication from Parimal publications Delhi or Nag Publications Delhi that also have some Samhitas and Barhmanas in mool form.
I hope it helps and wish you best in enjoying the beauty of Vedas :)