We don't have synonyms for lettermen yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are lettered, letterer and letterman.
(n) :
(US) A student who has attained a specified level of participation in a sporting or other activity, and is awarded a cloth “letter” to be affixed to an item of clothing.
(n) :
(US) A student who has attained a specified level of participation in a sporting or other activity, and is awarded a cloth “letter” to be affixed to an item of clothing.