We don't have synonyms for punkin yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are punkie, dunkin and junkin.
(n) :
(dialectal) Nonstandard form of pumpkin. [A domesticated plant, in species Cucurbita pepo, similar in growth pattern, foliage, flower, and fruit to the squash or melon.]
(n) :
(dialectal) Nonstandard form of pumpkin. [A domesticated plant, in species Cucurbita pepo, similar in growth pattern, foliage, flower, and fruit to the squash or melon.]