Since in the past Explorers have never found Pumpkins and they will be this year, I've taken the available data from the test forums and calculated how many pumpkins you can expect each Explorer to find on average in one day assuming your are searching 24/7.
Short 10.4
Medium 8.4
Long 6.6
V.Long 4.72
P.long 5.2
Note: Scouts and Experienced Explorers will find twice these numbers, Lucky's three times as many.