Those that make hafrashes challah by matzas for Pesach. Or a man that is nohag like it says in Seforim (Siddur of the Yavetz and others) to make hafrashes challah in the house once a year. May he make a shecheyanu? Is there anyone that speaks about this shailo?
I don’t know of sources for this specific question, but it is apparently similar to the general question of making a shehechiyanu the first time that a mitzvah is performed.
This question is discussed by the poskim in siman 22 conerning tefillin (the Ba’al Ha-Itur is cited by the Shulchan Aruch as ruling that shehecheyanu is not recited; the Taz writes that a berachah is recited on every new mitzvah that a person performs, and the Gaon explains that this is a dispute between rishonim; see also Yoreh De’ah 28 and Shach, there, concerning the mitzvah of covering the blood after shechitah).
The opinion that maintains that no berachah is made apparently maintains that the shehecheyanu blessing is only recited on those mitzvos that recur in regular intervals.
For taking challah, or taking terumos and maasros and so on, no berachah will therefore made, because there are no regular intervals for the performance of these mitzvos.