The Japanese Journal of Archaeology is available online, in English, open access: http://www.jjarchaeology.jp/contents/archive.html

Also many Jõmon sites have good websites including English-language materials, such as

https://www.akarenga-h.jp/en/hokkaido/jomon/j-02/

https://jomon-japan.jp/en/

http://www.dil2.sakura.ne.jp/eng/index.php/en/research/jomon-archaeology/16-research-e/14-japanese-prehistory

Also for what it's worth, the Wikipedia entry for the Jõmon period is good, and mentions the key texts on the period in English.