(def many-s [1 2 3 4 5])
(def many-p [:a :b :c :d :e :f :h :i :j :k :l :m])

(let [select-num 3
      s-picked (->> many-s
                    (map #(repeat select-num %))
                    (apply concat))]
    (map #(list %1 %2) s-picked many-p))

;;=> ((1 :a) (1 :b) (1 :c) (2 :d) (2 :e) (2 :f) (3 :h) (3 :i) (3 :j) (4 :k) (4 :l) (4 :m))