Ace Seeds have many old school strains, not far removed from native landrace varieties.
I recently tried "South Mountain Golden" bred by Xtreme Seeds and was super impressed with this old school Mexican Sativa that is just dynamite.
Barneys Farm also have many "traditional" strains.
Mandals Seeds also have many strains that are unique and far removed from any cookies/dosi/zkittlez/gorilla hybrids and will certainly knock your socks off potency wise and could also be classified as "traditional". After being involved with cultivation for medical reasons for close to 40 years, Mandala are at the top of my list for no nonsense quality products that offer something actual and special that just isn't found in modern hybrids. Their "grow guides" on their website also has a ton of no nonsense, practical and in depth information.
Another "quiet achiever" with outstanding products is Sweet Seeds.
Hope this helps, Organoman.