None of the verses in Numbers or 1 Sam. or Ex. say anything about tenple virgins. What are noted is women serving or gathered outside the tabernacle. Josephus says nothing about temple virgins and the reference to the Mishnah?
“(5) Rabban Shimon ben Gamliel says
in the name of Rabbi Shimon the son
of the deputy [High Priest]: The
curtain was one handbreadth thick and
was woven onto seventy-two threads,
each thread was braided from
twenty-four threads [consisting of six
threads of blue wool, six of purple
wool, six of crimson wool and six
threads of linen]. Its length was forty cubits and its width was twenty cubits
[corresponding to the dimesions of the entrance hall] and was made out of
eighty-two times ten thousand [individual threads]. They would make two [new]
curtains every year [which required immersion to sanctify its use for the Temple]
and three hundred priests [not to be taken literaly, rather meaning a lot of people]
would immerse it.”
Where are the temple virgins?
Marshall can think he knows whatever he wishes but so far the only basis he’s given is unreliable tradition. If that’s enough for him...then it is.
On the Mishnah, we are dealing with a variant reading.
(30) Threads, or according to others, denars in value. Another reading is ( ,uchr ) ‘damsels’, instead of ( tuchr ) ‘ten thousand’; i.e., it was woven by eighty-two young damsels.
http://halakhah.com/pdf/moed/Shekalim.pdf
Marshall quotes many more traditional sources beyond the Mishnah. And why is the Jewish tradition all of a sudden "unreliable"? We would not know nearly anything of the Judaism of the Second Temple period if not for it.