What is the source, (if any), for standing during ברכות השחר (from אשר נתן לשכוי through הגומל חסדים...)?
If citing a source from a Sefer please try to quote the words of the Sefer, rather than just the source location מראה מקום.
When it comes to standing for Birkat Hashachar, the following sources write that one should stand:
Ishei Yisrael 5:14 writes that some have the practice to stand.
Piskei Teshuvot 46:3 writes that the Ashkenazic minhag is to stand and a person shouldn't deviate from that practice unless they are sick or old.
The minhag to stand is sourced in the Mekor Chaim 46:2 . . .
And Siddur Yaavetz (prior to Netilat Yadayim in the morning) instructs standing for all b'rachos in general, unless the subject of the b'racha involves a different posture, in which case one should assume that posture instead. This would indicate that one should stand for those birkos hashachar that do not specifically refer to an activity that isn't done while standing.
(Halachipedia footnote 13)